Supreme Commander creator Chris Taylor has big ideas for Supreme Commander 2. Ideas involving extra factions. Thing is, he can't execute on them. Not yet, anyways. Because modern PCs, with their SLis and quad cores and whatnot, just aren't capable of doing what he wants them to do:

... the only thing stopping me from doing it [adding new factions] on any sequel is memory. I've been told by my engineers that for Supreme Commander 2, I don't have enough memory in a PC with 4GB of RAM to have more factions.

I'd like to think he's joking, but after what they pulled on the first Supreme Commander, he may well not be. And if not, anyone wanting more SC factions (and I bet loads more stuff) will just have to wait for the future to become the present.
Taylor: Hardware stalling Supreme Commander 2 [PC Zone, via CVG]