I reckon DA2 will have nothing to do with the 'hero' from DAO, with only a few people making cameos or actual appearances, they will probably go with the route they have with ME although I think might be a bit tougher for DA as there is more choices for people to make.
I agree with Magor that whilst Morrigan will no doubt be in it, Flemeth has just as much if in some regards more a chance of being in it because if what Morrigan said was true about her then it doesn't matter if you killed her or not.
The interesting thing about Morrigan is that if you went down one of the conversation lines during the ritual conversation she does state "if after you have defeated the darkspawn you come looking for me, do so at your own peril". I reckon THIS will be the closest we get to our current 'Hero' being in the story in that they will be dead by Morrigan's hands (akin to how the other origins tended to play out when you came across some of their story arcs).
With regards the 'Old gods' the one thing to remember is that there won't be another Blight for a good bunch of years, remember it was 400 years since the last one during this game and Riordan does state that it takes a while for them to grow and I really don't think they will do another 'Grey Wardens uniting the land versus a Blight' story again. That was done in Origins, Thedas is not just about the blights. There is plenty of other bad folk for people to be going up against.
I reckon Nevarra will be the next setting, as much as Orlais stands out, I also reckon it will be set at least 30 years in the future. In the two endings I've seen so far it has hinted at some of the stories it mentions as being quests for 'other' heros and that this heros story ended when the archdemon was dead. With regards the DLC for DAO, that is all set before the final battle, though the really odd thing is it must have all occurred in two or three days because if you say no to the ritual, Morrigan isn't in your camp in the post-epilogue save.
I reckon only a handful of the current NPCs will make either a big appearance (Morrigan and Flemeth) or a cameo/mention appearance (Alastair, Anora, Loghain).
I can't see Leliana or Wynne, I reckon their stories ended with DAO too, even if you did keep them alive. Whilst Wynne's epilogue did mention going off to explore the world, her time was coming to an end and the epilogue for Leliana even if you weren't in a romance with her indicates her connection to the hero.
I actually can't see how some of the other party members would get a mention or appearance other than maybe Shale... oh and maybe Sandal (because as him and Bohran are in the camp, I consider them party members of sorts)
Enchantment?
Think Nevarra will be the next location and the story will revolve around the Dragons coming back in full force and the it could possibly end on a cliffhanger with the hero managing to stop one bad person but a more dangerous threat to the world revealed.