What is needed is *the ability to import your previous AC files*. Think about it, it could be a true sequal. Maybe they could have it so you move out of your previous village (that you did in the original game) - and move into a much bigger "town". Then they could make it so your previous friends from the previous games write you letters and send gifts etc - referring to past experiences from the original, or maybe even pay you a visit. That would be sooooooooo cool!
On top of that, I'd like to see even more connectivity, because it was connectivity that really made the original great. More e-reader cards, more everything. Maybe online play - I'd say the original AC was really begging for online but nintendo really did well working around this by having as larger sence of community as possible with an offline game, if you get me. But it really could've done with online and don't rule out GC being online in the future, its still not closed - it could still happen. And when nintendo get right behind online play, they'll do it better than anyone else - trust me.
Although a game like this could backfire should they release it in Europe (which I'm pretty certain is the plan this time). If it links with the previous game, then people who imported it would import it again. Unless NOE just accept their losses and let the european version be compatable with the american files - which to them would be admitting defeat. But when nintendo of Japan makes these games, they work to make the best games possible, so I doubt they wouldn't do it like this just to keep NOE happy - NOE really not having much to do with NOJ. But whatever they do with AC2 - I'm sure it'll be great!