I've always been thinking about a game in which you can visit all 5 (6) regions. Short summary: Team Rocket should be the villainous team, because Giovanni got more potentional during his battles in the PWT. Every region has his own Admin. You start as a trainer in Aspertia City and chosse your starter in Nuvema. After defeating Rocket in Unova, you have to travel to Kanto by plane. From there walk to Johto, from Johto to Sinnoh by boat and from Sinnoh to Hoenn by boat ass wel. You have to defeat Rocket Admins in eevery region and the grande finale should be on Mt. silver where you battle Giovanni. The level curve isn't a problem if you just hand over your Pokemon to the regions proffesor.