I'm inclined to expect AC2 sooner than that if we assume a few things. First, that Kunos and their parent want to get cash flowing sooner than later. Second, that they will mostly re-use existing assets like track and car data. Third, their core team will be free to work on the game itself while additional content creation and other work is taken on by the expanded team. Fourth is that they'll shoot for at least a current gen release.
As you mention, there shouldn't be any big technical issues with multi-platform release. So if it makes sense from a timing/effort perspective, release a scaled version of the game for current gen consoles, rake in some cash, and then make AC2+ a release title for the next gen, hopefully coming pretty close to what was available on PC since several months before the initial console release
Anyhow, this is the strategy I imagine the Digital Bros bean counters proposed while shamelessly sporting this face: