I'm kind of obsessed with the idea of artificial people.
When I was very little - probably 3 or so - I remember seeing a movie that I just remembered as "Conrad," though I believe it was actually "Conrad: The Factory-Made Boy," in which a little artificial child is delivered to a family accidentally. I remember nearly nothing about the plot of this movie, except that this little kid (who was the protagonist if memory serves) was a good boy who just happened to have come out of a cylindrical package (I remember vaguely that he had been in some kind of powdered form that made a kid when water was added, but it's possible I 100% invented that).
Star Trek: The Next Generation also premiered a year after I was born, and while I don't think I started watching that until I was at least a little older, it was the first prime-time TV show I remember regularly watching (though if memory serves, The Simpsons, which was then an even bigger cultural phenomenon, came on at 7:30 after Star Trek started at 7, so we'd often miss the back half). On that show, I loved Data, the android crew member who was on a constant quest to develop true "humanity."
I don't know whether we'll ever be able to know for certain that an artificial intelligence we create is sentient (i.e., has a conscious, inner experience of their thoughts and perceptions) though, of course, we can't be 100% certain that the other humans we speak with do (though I think the vast majority of people assume they do).
In a fantasy world in which "souls" are empirically provable, there's a convenient way to make a clear distinction between a machine and an artificial person.
Given my Jewish heritage on top of this, I have a soft spot for Golems in fantasy. The folklore surrounding Golems is a bit complex, but my understanding of it is that, according to the Torah (what Christians would call "The Old Testament," essentially) God first created humanity out of clay. Thus, a sufficiently righteous person, who had the wisdom and knowledge to do so, would be able to imitate God in this act, bringing lifeless clay to a semblance of life. Obviously, no human could be as perfect as God in doing so, so it's not like this creation would be a full human. But the version of the story of the Golem as I understand it is that this is a righteous and sacred act - a good deed. And because the Golem is created in a righteous act, the Golem itself can do good deeds.
Again, there are a lot of versions of the story that might contradict one another, but that's the version that I prefer.
Many of the playable races in the Eberron setting are, I think, meant to take creatures that have historically been just monsters (not necessarily evil ones) in the Monster Manual and turn them into playable races. Shifters give you something akin to lycanthropes. Changelings are playable doppelgangers. And Warforged, as I see it, are playable golems.
Eberron borrows a lot of 1930s pulp genres as its inspiration, and the Last War is meant to be someone analogous to World War 1. While I think some post-WWII elements bleed into the story (Film Noir detective stories are something I tend to associate more with the late 40s than the 20s and 30s - I guess given that we're actually in the 20s again I should specify the 1920s) pulp literature certainly did become really prominent in that era. And I think the Last War - not a decisive defeat of some great evil but a kind of grueling struggle that ended without any of the inciting causes truly resolved - does seem more akin to the First World War than the Second.
But the Warforged story is closely tied to that idea of the Last War. In Eberron, the entire race is only a little over twenty years old. No one has any idea how long a Warforged will life "naturally," because they've only been around a couple decades.
On top of that, as vestiges of a conflict that is now over, the reason they were created is no longer around, creating a serious lack of purpose. On top of that, their lack of physical needs has given others cause to hate them for being the cheap labor that displaces organic races.
All of this combines to make a really interesting story for Warforged characters in an Eberron-based campaign. But at the same time, it ties them very closely to Eberron as a setting.
Indeed, the very name of the race ties it to that backstory - they were created (forged) in order to wage war. Or even that they were created amidst a war.
Mordenkainen Presents: Monsters of the Multiverse is a revision to many monsters and playable races in 5th Edition D&D. I was actually somewhat blown away by the number of races in the book - I believe it's about 30, which goes beyond simply reprinting the ones found in Volo's Guide to Monsters and Mordenkainen's Tome of Foes, but also adds those from Elemental Evil's Player's Companion, as well as a few others that are from adventure books (the Fairy and Harrengon from Wild Beyond the Witchlight, for instance) as well as some that are from campaign setting books - we're getting the Centaur, Minotaur, and Satyr, for example, which saw publication in the Ravnica and Theros books (only Theros for the Satyr). We actually aren't seeing the Vedalken, Loxodon, or Leonin. I have a suspicion that there's some complexity - whether legal or philosophical - about putting races that originated in Magic the Gathering being put in a setting-agnostic D&D book. (Centaurs, Minotaurs, and Satyrs of course all being directly pulled from Greek myth).
I don't know the precise legal status of Eberron as a setting - Keith Baker did release a book for 5th Edition that was not published by WotC, so he may retain some rights to the setting. I know that the Hickmans retain some ownership over the Dragonlance setting. Still, two races from Eberron - the Changeling and the Shifter - are being published in Monsters of the Multiverse. But I was kind of shocked to discover that Warforged are not. I was surprised by this because I think the Warforged are the most popular and iconic Eberron race.
Now, here's the massive caveat that I didn't even think of until I started writing this post: Monsters of the Mulitverse is forward-looking to the 2024 core book release, which will give us either 5.5th or 6th Edition D&D. Given the depth of the revisions to the races I've seen in the book, I think that WotC is going to be doing some pretty thorough work to revise the game for those 2024 books. And that could mean that the lineup of playable races in the Player's Handbook might change.
For example, the 4th Edition PHB did not have half-orcs or gnomes, but they did have eladrin as a whole separate race from elves. For those of us who started off in 5th Edition, the notion that dwarves, elves, humans, halflings, dragonborn, tieflings, half-elves, half-orcs, and gnomes are the be-all and end-all of "standard" races you'd find in the PHB, might seem really set in stone, but of course, it could change.
Thus, to conclude this caveat: it's possible the reason for the absence of Warforged in Monsters of the Multiverse might actually be that they're going to be in the next PHB.
But, let's assume they're not.
One thing that WotC seems to want to experiment with in the future is diversifying the creature types of playable races. Up until I believe Guildmaster's Guide to Ravnica, every playable race was considered humanoid. Then, Centaurs were given the Fey type (which is funny given that the Monster Manual describes them as Monstrosities). Fey, it seems, is a type they're comfortable giving to playable races. So we've seen this applied to the Satyr, Hexblood, and Fairy. We're also going to see Changelings in the new book given the Fey creature type as well.
Before the release of Van Richten's Guide to Ravenloft, the Uneathed Arcana for "Gothic Lineages" presented a bizarre proposal: hybrid creature types. Dhampir were both humanoid and undead. Reborn could be humanoid and either undead or constructs. And Hexbloods were humanoid and fey.
I think the reason for this was healing spells. Many of the spells in 5th Edition that can restore hit points to a creature specify that they cannot do so for constructs or undead creatures.
But, as it turned out, this solution probably caused more problems than it solved. First and foremost, the rules didn't act the way they seemed they should. After all, D&D is a modular "flag & check" system (I have no idea if that's a real game design term, but I'll explain.) A lot of labels in game - things like creature type or damage type - don't have any innate rules to them, but they create something that other things can check for. My fireball does 8d6 damage, and most of the time it doesn't matter that that's fire damage. But when I use it against that horde of scarecrows, who are vulnerable to fire, suddenly it matters quite a lot.
So, the first problem that this proposal created was that, you would think, if my Dhampir was both humanoid and undead, a spell like Cure Wounds that doesn't work on undead creatures, should simply check to see if my character is undead, which should come back yes, and then fail to work because of it. Instead, the intention was that it would see that, oh yes, in addition to being undead, I was also a not-undead creature type, and therefore that "humanoid half" was a valid target for the spell. It's... not elegant.
But on top of that, it also opened a whole can of worms. If hybrid creature types were possible, shouldn't we then go back through and change, like, a lot of them? Shouldn't Genasi be humanoid/elementals? Shouldn't tieflings be humanoid/fiends? And, of course, shouldn't Warforged be humanoid/constructs?
Obviously, being a humanoid if you might one day want to receive a healing spell is a big advantage over being a construct. And, on a philosophical level (bringing it back) the fact that Warforged are humanoids seems to strongly imply that yes, they are sentient, conscious beings with an inner life.
But perhaps we're looking at more adventurousness with playable races. In the "Travelers of the Multiverse" Unearthed Arcana, there are a number of eye-raising playable races that go beyond humanoids and fey alike. Plasmoids have the ooze creature type (in our new Spelljammer campaign, one of our party is a Plasmoid Rogue who's going Soul Knife so they don't have to carry any equipment and can thus make full use of their amorphous form). Thri-kreen are monstrosities (ironically, given that they're humanoids in the Monster Manual - another Centaur-like inconsistency, though even less expected.)
And then we have Autognomes. Actually, this is particularly funny as someone who plays World of Warcraft, given that not long ago, Mecha-Gnomes were made a playable race in that. However, Autognomes are not cyborgs, but are in fact fully artificial beings constructed by gnomes. While they share some traits with Warforged, Autognomes are, in fact, fully constructs. They have a special feature that allows certain healing spells to work on them, but it's a pretty conservative list: just cure wounds, healing word, and spare the dying. This rider does help them out a lot, though I think only at low levels. By the time you get to tier 3 and 4, missing out on spells like Heal, Mass Heal, Power Word Heal, Healing Spirit (that one's even pretty low level) can be a real liability.
Frankly, I think that Warforged get the better deal out of this, even if their mechanical nature is rendered somewhat less strongly enforced.
Obviously, if Autognomes get officially published, we haven't seen what their final version will look like.
But I do think there are some interesting game design questions to be asked regarding artificial beings. I was actually a little disappointed that, for example, a Reborn character doesn't get to count as undead. In the case of creature types like Fey and Monstrosity, there aren't many spells or abilities that affect those specifically - in many ways, it's just an asset as you become immune to Hold Person, Charm Person, or Dominate Person. Perhaps the issue is not with the idea of having a player be Undead or a Construct, but just that the decision early on was made to make nearly every healing spell worthless to such creatures.
The concept of artificial people, I think, should not be limited to Eberron as a setting. It's a potent and really exciting concept that could work in a lot of settings. In my own homebrew world, rather than a maximum age of 20-something, given the development of the Creation Forges, instead the minimum age for Warforged is over 20,000, because the civilization that created them collapsed and the vast majority of them were locked away, unconscious, in hidden vaults during the intervening millennia. (This also lets me play with another of my favorite concepts: the Time Abyss. One of the Warforged-founded monasteries in my setting has a "statue" of its founder, who is, in fact, a Warforged who has remained in deep meditation for thousands of years.)
I think Warforged would work fantastically in the science-fantasy of Spelljammer. They could be inhabitants of Mechanus in Planescape. They could be (are?) beings built in the Age of Arcanum on Exandria, or could be relics of the Netherese civilization in the Forgotten Realms.
So, I guess fingers crossed that the reason they aren't in Monsters of the Multiverse is that they're getting an even bigger spotlight on them when the 2024 core rulebooks come out.