So, I want to talk about the Psyker abit.
Mearls take on the Psyker and a more advanced class design is interesting. Essentially, we get three Paths at 1st level. While this may sound like subclasses, they aren't; they only give benefits at their level
and modify certain other class features. Mearls has mentioned he wants the Psyker to occasionally give out new feature menus at higher levels; essentially, you have several smaller subclasses that you'll choose from as your Psyker levels up.
I love this design and it could be applied to some of the base classes in amazingly cool ways. The Sorcerer, Ranger, Monk, and Warlock would be great for this model. You aren't a Warlock of one thing, but you've made several pacts -- some big, some small -- as you've leveled up. Your Ranger doesn't have a subclass, but instead a bunch of tricks and skills picked up in the field. It's wonderful in that it opens up single-class ideas that don't always produce ready subclasses and turns the base class idea into something customizable enough to match the class - subclass paradigm.
I am eager to see more of the Psyker. I think it would be a cool model for some of my content. I've even theorycrafted a way this model could contain all the info necessary for a stand alone, one-class duet/solo game. It's so rich, and I was really missing this kind of mind-opening variety from WotC's mechanics...I'm glad
@mearls has continued where he left off years ago.