Class Feature Revisions in Tasha's Cauldron of Everything

 One of the features announced with the upcoming new rules book for D&D 5E goes beyond subclasses, and alters the classes themselves.

We got an Unearthed Arcana article a while back that set forth some of these ideas.

One of the biggest new features is Spell Versatility, which applies to pretty much every class (classes that prepare spells get "cantrip versatility," which effectively makes this umbrella go over every magic class). Basically, when you finish a long rest, you can swap out a spell you know for another from your class spell list.

This is a pretty great way to let players experiment a bit with their builds and not feel like they've made some huge mistake for picking a cantrip or spell that looked like it would be useful, but isn't, actually (True Strike says hello!)

The Ranger has also gotten some profound re-works to their level 1 features - Favored Terrain and Favored Enemy can be swapped out for Deft Explorer and Favored Foe.

The former is a more broadly applicable set of bonuses to your environmental exploration capabilities, letting you clear exhaustion more easily, giving you a climbing and swimming speed, and a few other bonuses.

Favored Foe essentially lets you use Hunter's Mark like a class feature, and removes the need to maintain concentration on it (you get a limited number of uses, but it's still probably better than the number of spell slots you have, at least early on.) I'll definitely say that for the character I might multiclass as a Ranger/Barbarian, this change would be insanely welcome (as Raging breaks concentration on spells.)

Likewise, the Beast Master subclass has gotten a new replacement ability that lets you call forth a "Beast of the Air" or a "Beast of the Earth," which, along with scaling with your level, also lets you resurrect it easily, which I think should make the subclass a bit more appealing. Most importantly, you can have these attack with your bonus action, making the subclass feel a little more like, you know, people assumed it would.

Caster classes get expanded spell lists, and classes with fighting styles get new styles and get the ability to swap styles when they gain a level.

One new Warlock invocation that I think is important to note is Eldritch Armor - which is that you can use an action to touch a suit of armor and immediately don it, and you are considered proficient with it while wearing it. While I'm sure the idea here is to let a strength-based blade-lock (it's a Pact of the Blade exclusive) wear heavy armor, I also think there's some hilarious potential for larceny with this invocation - you could walk into a store filled with fancy magical armor and just "whoops" touch a set of +2 Adamantine Plate Armor, cast invisibility on yourself, and run the hell away. Still, this is an effective way to give Warlocks proficiency in heavy armor without requiring most to take two whole feats just to get there (Hexblades would need one.) Plus, it would mean that a Warlock of this variety would be an ideal defender if your DM is a stickler about not letting you rest in heavy armor - once the alarm bells go off, the warlock just slips the armor on for their first turn, bonus actions their weapon in hand, and they're good to go.

The big question I have about these features is how it will play at a DM's table. As a DM myself, I'm likely to just say that anything found in Tasha's is fair game, and if you want to use these features in addition to or in place of stuff from the PHB, I'll allow it.

But I do think that it will require some re-learning of class features for players and DMs. Still, after 6 years, it'll be nice to see some broken features and classes finally work well.