I would think that, with the massively long wait for Rome just to come out, that the expansion is a way off, and I don't think they'll hesitate to make big changes, even if it takes a long time. Punctuality doesn't seem to be a concern. Probably
1. Different starting times.This annoys the hell out of me, and could just be wishful thinking. This will coincide with:
2. Mini-Campaign. Since Total War is always moving backwards, I'm betting on Alexander and that whole thing. Money in the bank.
3. Hopefully they'll do new naval battles, but it is severly doubtful. Not because of time or effort, but through three games they still haven't noticed it's a problem. Doubt they willl now.
4. Probably not a lot of new units, if any at all, would be with the mini-Alexander-Campaign only.
It'll definitely be Alexander. Just decided for sure.