Don't expect it to be coming any time soon, as Black/White are still on their way for North America and Europe.
The first thing that comes to mind is 3-D Pokemon battles, something totally different considering Pokemon has long stayed close its 2-D roots. So who knows? I don't think there will be multitudes of new Pokemon, but if there is a new region, there certainly will be some. I have a feeling a lot of old Pokemon will make appearances. This game might be for 3DS what Diamond/Pearl was for DS. Then again, having all the regions together (as unlockable content perhaps) would be absolutely mind-blowing. As for storyline, I think it will be focused on the familiar type of bad guys, but with new twists.
But with this revelation a few weeks ago, it's good to know that the Pokemon game series isn't over just yet.