The point behind FireRed and LeafGreen was to bring Kanto into the third generation, since there was no backwards compatibility like Gold and Silver's Time Capsule (a feature excluded due to radically new mechanics between the two). HeartGold and SoulSilver were made in Gen IV because Johto's absence from Gen III made most second generation pokemon hard to find still, despite the few in Gen III and FRLG's small sampling in the Sevii Islands. The funny thing about ORAS is that while Hoenn in full 3-D is great and has been something people have been excited about, there was no real technical reason to remake the Gen III games, at least not nearly to the degree that warranted Gen I and II remakes.
I think that as handheld console technology improves, the idea of one region being big enough to contain ALL pokemon is feasible. Of course, to make it interesting, it'd also be ideal for GF to step up their game in terms of what makes a region. Maybe sixteen gyms, like in (Heart)Gold/(Soul)Silver, except in one huge region instead of two. Otherwise, we would be slated for Gen IV remakes, which are wholly, entirely unnecessary.
Basically, a literally huge Pokemon world, but one that doesn't feel empty. The only downside to a bigger region would be a longer story, which isn't necessarily a problem, but may cause some issues with level scaling. But you see, by including all possible pokemon, they will have no reason to develop remakes of games whose region's pokemon got the shaft in the regional dex selection process.
tl;dr: Remakes are the result of exclusivity and neglect in regional dexes, and are dictated by the necessity to reintroduce pokemon from older regions. Now that regions hold more pokemon than ever, and may one day hold EVERY pokemon, remakes won't be necessary at all.
