It's probably way too early to talk about another expansion, anyway, what would you want in the next expansion (Or MB2?).
I hope the next expansion adds: A Japanese-Chinese-style faction on an island that is actually populated by Japanese/Chinese looking people instead of white people, boats, naval combat, better terrain graphics, a lot more/better quests, more companions, multiplayer navel battles, a bigger map, bigger multiplayer battles, more armor/weapons, better sound, more food items, more buildings for towns/villages/castles, more things to do with your own player-faction.
I'll add a much more detailed explanation of the new faction idea later.