I want a larger variety of pokemon available from the start.
If the next game let you go from Region to Region in the starting phases of the game, not later on after you beat the giant ass championship, then it would make for some extremely interesting playthroughs.
Sure you would not be able to explore all the regions entirely from the get-go, you'd need to find HMs and get the badges. Each region would have their own set of HMs available to find, and Gyms with badges to let you use those HMs, so if you prefer 1 region you could stick to it no problem.
You could also go from region to region at any time in case you simply can't find the right pokemon to fill that last spot in your team, like a good lightning type with ranged lightning attacks or somesuch.