I agree too that it will and for the most part should be a careful exercise to allow outside content into a new released title. I'm not sure how good it would be to have the sheer amount of "garbage" content muddying up their pristine new baby. I mean people are making good products these days but you know what I mean. As fun as T-Rex's are or shopping carts or nude guys riding a bar bell, really don't know if that's the visuals they want. lolI would also expect to see modding available in AC2, however I suspect it will be heavily locked down to approved and verified content, something like the Steam Workshop with only scratch made or authorised conversion mods that can also be released on consoles as well. Basically I expect it to be limited to Racedepartment type content only and I'll be massively surprised if they don't do everything in their power to make it impossible to port over cars and tracks from other games.
I guess we'll see in time, not that I particularly care, I've sunk so much time into modding AC1 that unless there's a button to import all AC1 cars/tracks into AC2 then it's completely uninteresting to me. My only real hope is that they don't release AC1 updates to break CM and CSP in an attempt to force people onto the new game, something I can see happening if AC2 is released in the state of most modern titles (i.e. a barely beta tested broken mess of bugs and unfinished content with lots of promised updates and DLC).
I see no reason that they'd break AC1. It's what has made them who and what they are today. That would cause an irreversible rift that there just isn't any logical reason for.