Only way that's going to happen is for Groudon/Kyogre/Rayquaza, and I don't think Kyogre and Rayquaza wouldn't have much trouble traveling to another reigon. Groudon however could have difficulty, but they would just make up some reason like "he made more land and walked across in search of Kyogre" or something like that. They're trying to make all the 3rd generation pokemon available through the newer games since the DSi has no GBA slot, so maybe a poke-radar but going to Hoenn seems unlikely. It would be pretty cool to travel to all the reigons and get all the badges, like in the original G/S/C though. If HG/SS really had all that D/P/Pt would suck and be good only for getting the 4th gen pokemon 