Blackwarder
Adventurer
I mean, obviously, I don't expect a solid answer, but having followed 5E for it's entire history, it seems like two things they used to talk about quite a lot have gone MIA - specifically PrCs/Paragon classes - i.e. classes you go into at a level above first, and one thing Mearls was talking about a fair bit a while back - classes which basically simulated a multi-class combo, like Fighter/Mage (3.XE was full of these, for basically the same reason 5E might need them). The last MC rules I saw still kind of necessitated them for some character concepts.
Do we know anything about this? Have they been casually mentioned in Mearls' twitter or an interview I didn't read hard enough, or is it radio silence on them? Which doesn't mean they won't be in the PHB/DMG, of course, but I do wonder...
Thanksfully PrCs has gone the way of the Dodo, iirc in the last Q&A video chat Mike Mearls said that they want to take a wait and see attitude when it comes to PrCs and take another look at them several months after the release of the game.
Don't expect to see any PrCs in the Tyranny of Dragons adventures, they started working on those adventures more than a year ago, if there were PrCs in there than MM would have said something else.
Warder