I'd like some way of resolving Jack's situation at the end of situation 8 - both the Americans and Russians were after him and he was in hiding. I appreciate that they can't spend a whole 12 episodes dealing with this storyline but I'd like a little more than a throwaway line to explain it. I assume that some situation will arise that only Jack can resolve and the US government will have to pardon him to get him to deal with it.
Chloe is bound to be a cert to return, Kim is also a likely. I'd love to see Tony Almeida come back after they completely shafted his character (crappy death in S5 and then making him a villain in S7) but this might be even harder than explaining Jack's return.
If early reports are true that they're jumping ahead several years again (meaning the terrorists will have laser guns, jet packs and robotic body parts), then lip service to how season 8 ended will probably be the case.
Unless it opens with, say, Jack and Tony being let out of prison because only they can stop a certain threat.