So a small area of Johto is potentially based on Shikoku? Will the rest of Honshu and Shikoku be used or will other International areas be translated into a Pokémon game? 

Shikoku is not really big enough for a whole game, and I'm not sure how they'd tie in another part of Honshu while keeping the game interesting. My guess is that we're going to see some international areas for a while. London is a possibility, but Nintendo and the Pokemon company have a history in the American North-West (Pokémon USA and Nintendo of America are both based in Washington state), so maybe a Seattle-based game is in the future.

If London was included then Kent would surely be included as well. Cricket Players would be primary figures for the game. Washington is unlikely in my opinion, though some aspects are suitable. British Columbia has a higher chance. 

One request for Pokémon Black/White is that Game Freak include the Thousand Islands in some form. I crossed the Ontario border to New York and I can state the view is outstanding, Niagara Falls potentially as well (of course, I have visited it as well). Though these locations cross with Canada and are situated far away from New York City.   

Kinda looks like New York that way, with the central island surrounded by two rivers, though the mountains are out of place. Could possibly be the vicinity of Vancouver, as well, that sould suit a lot of the topography better.

After studying Vancouver I agree. They are similar in Shape, however Mountain Ranges of British Columbia are far away from Vancouver (such as the Rocky Mountains). Vancouver is also facing the west.

It doesn't have to be just Washington. The entire former Oregon territory would be a good region, with lots of forests, coasts, big cities, huge mountains, a bit of the Great Basin to the South-East, natural parks, etc. I'd imagine it would be pretty similar to Johto and Kanto, just with a different orientation.