Predictions on the Crimsonwood Keep expansion?

Those are both the most likely ones at this point. Jack said he'd come and he's been in there before. Lukan lived his whole life there, so that's another possibility.

It's no doubt that there'll be another chain of quests when the second part is out dealing with the removal of the barrier. I'm thinking we'll need the help of someone very powerful to do that. Perhaps consult Ridley somehow, or as you suggested, a new person.

Adding someone new is a little too...convenient though. I think the barricade brothers will get through somehow. Probably through the same backdoor jack got out of.