I'd like to see one. I'd also love to see all regions reachable in one single game. It'd have to be a huge game, but I still think it should happen eventually.
Isn't it just the real world (mostly)? I remember the first few gens were actually loosely based on areas in Japan that actually fit over different chunks of the country if you rotated them properly.
There's not really any need, all Pokemon locations correspond to real world locations, it's better to just imagine that the trees and ridges that normally block you aren't there in the 'real' Pokemon world.