As you are probably aware, every Pokemon game has been set in a bite-sized version of a real-life region in Japan. Of course, after 4 generations of Pokemon there aren't a whole lot of settings left. I've color-coded a map to show you what's been used so far, and have decided what I think is the most likely region in which you can expect the new game to take place.

Note that the Kyushu region, the blue one for RSE, was rotated 90 degrees counter-clockwise in the game.

I think when it comes down to remaining geographically interesting locations, the most likely candidate for the new game is a combination of two geographic regions. These are the Chugoku region, which is the part of the mainland of Japan between RSE's and GSC's regions, and the island/region of Shikoku south of it. The combination of these two regions would yeild a lot of geographic diversity, including mountains, volcanoes, temples, jungles, oceans, large modern and historic cities, planes, a plateau, and even a desert-like 30km stretch of dunes.

So if you were wondering where Pokemon was going to be next, I'd put your money on this.

Hm, I thought I was the only one thinking the next region would have to be two combined from Japan.

Damn, I never really noticed.

It wouldn't have to be if there were interesting single-regions left, but there really aren't. Frankly for generation VI I expect them to leave Japan.

Really I'd think by Gen six they could have all of Japan, and start somewhere that hasn't been done.

My guess would be Tohoku.

That's really clever. Didn't realise the areas in pokemon were based on regions of Japan. I agree with your assumption but what about the 8 islands in the FR/LG 1st. gen updates. Where did they come from?

You'd figure Shikoku would be the obvious choice, since the last two represented Kyushu and Hokkaido

Shikoku would be too small alone. The regions in Pokemon are actually all scaled correctly for their size in the game. In other words, Kanto:Kanto is the same proportion as Sinnoh:Hokkaido. So Shikoku alone would be far too small.

@Son1x, Tohoku is about the right size, but far too geographically plain. It doesn't have enough interesting features to make for a good Pokemon game, and it's not set up to have much available in the way of water pokemon/ocean stuff, which is always important for a Pokemon game. It's also an awkward shape for the standard squarish Pokemon world map.

It has Sendai, more than enough
(yea, I'm joking)