Heinage
Khan
IMO (speculatory guesses)
-expanded UN
-Earlier choices for diplomacy / religion expanded (AP?)
-International Trade Routes? (One World?)
-Expanded Trade (Bonus Resources, finally tradeable?)
-Expanded Economics (A return of new and improved corporations?)
It is clear that every expansion pack with civ has added different civs and in additional leaders per civ.
I also think like G&K there will be improved AI.
I think I agree with everything you're speculating about here.
It's worth noting that if you currently check out the list of resources you have in your empire, it displays all the bonus resources and quantities (1 fish, 3 cows, 2 wheat etc.). I always wondered what the point was of that, but maybe it was coded in right from the start so that implementing corporations would be easier to do. That way you can have a similar corporations mechanic to what we saw in Civ IV, where having more of a certain bonus resource (and trading for it) has benefits for your empire (and whereever your corporation expands to). Why else show us the quantities of bonus resources?...
And, if One World does indeed turn out to be a second expansion, first of all, let me just say how happy I would be, and secondly, let me plead for an expanded UN in which we finally have resolutions to vote on. Surely that, together with international trade, is the quintessential part of "One World"...