I'm really pleased about this. It comes soon after I'd given up hope on the movie ever getting off the ground.
The more I think about this, the more I think that this is the perfect vehicle for a 24 return. A 2 hour movie is too short and would be shorn of the show's distinct identity. And, the excellent Season 7 aside, the series was running out of ideas to fill a full 24 episodes. 12 episodes, taking place at different times over the same day, will allow them to make for a leaner and sharper adventure. No CTU moles, love-lives of supporting characters, cougars, amnesia and other silly sub-plots.
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.