I'm personally hoping for something more detailed than just classes and races, especially since only Monk and Dragonborn are left from the PHB (Artificer would be nice, but not super crazy for me). However, if we get a complete list of subclasses and/or backgrounds that would be amazing and would really help me conceptualize my PC.
Aside from that I'm also curious about gameplay features. Most notably how resting will be updated as well as if the paladin oath criteria will be clarified.
