They might change things drastically, but they might not. I know that they've mentioned a few times the 'inconvenience' of SMN/SCH sharing attribute points and how that's looking like a problem to them now if they were to release new jobs from existing classes. I think they're regretting a few of the inflexibilites of the current armoury system. Aside from that, there should be a 5-10 (I'd guess 10) level cap increase, new skills/ traits to go with it, I suppose 1 more cross class slot for jobs (and 2 for classes), a new egi or 3 for SMN, new areas -- likely Ishgard and surroundings, which I suppose would be more of Coerthas, maybe Ala Mihgo and surroundings. It's all speculative, of course, because as you said they haven't revealed much of anything yet.