This is probably more of a 7th or 8th gen kind of thing at the earliest, but it'd be nice to see two sets of sequels to HGSS, one based entirely in Kanto and one based entirely in Johto, so that both regions can develop a sort of separate identity. Because let's face it, they both kind of feel like half a region compared to more modern ones like Hoenn and Sinnoh. But I doubt that'll happen anytime soon, HGSS is too recent a game and people are sick of Kanto after having it for 4 gens in a row. Anyway, here's what I think might happen in the immediate future (6th gen):
2013- XY (confirmed)
2014- XY DLC
2015- RS2
2016/2017- XY2/Z
2018/2019- 7th gen?
I think they might want to consider making Pokemon generations a bit longer from now on, considering that console generations are starting to get to be about 7+ years that would mean that either Pokemon has to follow suit, or we'd have to have multiple generations per handheld like they did with the DS. 5+ years is probably a reasonable length for 6th gen if they choose the former, because by then the 3DS' successor will probably be out around then. If they choose the latter, though, they can just bump up 7th gen to 2016/2017 and 7th gen will be the 5th gen of the 3DS, likely extending the 3DS' lifespan for a while after its successor comes out.