If we see a return to Japan, I hope that it includes the parts that have yet to be used too.
Or perhaps a region based on the Korean peninsula or eastern China would work nicely since they're Japan's neighbors. Kyushu (Hoenn) isn't all that far from the southern-eastern coast of Korea, so we could see a return of Hoenn (I wish) post game by ferry.
If Japan, I want to see us going up of Johto and Kanto's maps (which in real life this hypothetical region would be based on western Honshu). We could see the Sinjoh ruins returning to hint at a Sinnoh remake as well as continuity with HgSs.