Facetious answer; all of them.
Realistic answer;
I think I read somewhere that they aim to add all the PHB stuff, which is nice. That being said I would like to see a few non-PHB ones added in to even things out a bit. The cleric and wizard both get tons of subclasses but most of the other classes only get 2 or 3. A couple that spring to mind that I'd like would be hexblade or celestial warlock, scout rogue, divine soul sorc and conquest paladin.
Wishful thinking, but it would be fantastic if they could add in artificer, but maybe that is a job for modders later.
