The thing about Pokemon games is that they're timeless. Literally. I haven't beaten Black 1 yet, but I plan to, and then Black 2, then hopefully get a job, 3DS and X. I may not beat Black again, but I'll certainly play it to catch other Pokemon. To compare, I played Red and Silver from start to finish over, and over, and over again.
I don't know how many of you have played the original games, but I think the internet killed a certain aspect of Pokemon. It's now very easy to get ANY Pokemon you want through strangers online.. so that kills the "start new game, get different starter" aspect.
tl;dr - I think people will continue to play this generation to catch the Pokemon they haven't before and refresh their memories. A lot of people will buy the 3DS and then have 2 systems so they can trade with themselves.