It's now the middle of April, and thankfully we're seeing a more complete version of Legion now. With the addition of Destruction, all 36 class specializations are now in the mix. I don't know if Suramar has been opened up yet (I think not,) but one of the major set-pieces of the expansion, the Broken Shore invasion, is open for the Alliance.
I won't go into plot details, but it looks like this scenario will serve as a somewhat shorter equivalent of the Tanaan Jungle intro, ensuring that fresh 100s are getting gear that will let them keep up with those who are decked out in Hellfire Citadel stuff.
There are also a bunch of new UI elements. Legendary items (which are world-drops that work a bit more like Diablo III legendaries, altering specific abilities) are now listed in the Adventure Guide. Also, world quests that include world bosses, stuff going on in various zones, PvP objectives and other such stuff are also being introduced.
I believe all the dungeons are available (unless there's a missing Suramar one, though I'm pretty sure we would have heard about it by now.)
So there's not a ton left to add to the expansion at this point. Suramar as a zone is potentially a big one, and hopefully that'll make it in soon, but it does seem that while there's a bit of talent redesign going on at this point, it's mostly a balancing and polishing thing for many of the core game systems.
I'm still betting on a June release, though at this point that's starting to be somewhat soon. My hope is that we'll get a solid release date by the end of the month. I feel like two weeks for a pre-patch is generally what you can expect (Cataclysm was a special case because there was the pre-event as well as the Shattering itself) so hopefully we'll be seeing that somewhere around the release of the movie.
Anyway, some other fun tidbits from the patch: there's a new Beholder model for Warlocks (I think it's a Demonology talent... that I'll probably be taking) that looks a bit more Fel (purple/green) and tentacle-y than the Throne of Thunder one. Also, there's finally an updated Voidwalker model, in both standard and armored void lord varieties, which is good to see considering how apparently crucial their kind are to the Warcraft cosmos.
Here's hoping for a release date announcement in the soon-times.