Um...
1. No because this would give one more reason for people (and by people, I mean people with copyright on the pokemon games) to sue PU.
2. I'm not sure if most people want to go back to a place they already know... wouldn't exploring a whole new region not be more exciting and challenging? Plus it allows for more a custom game, since more quests can be implemented.
Next, there will be some sort of pokemon league as in a competition held intermittently and the title of champ (if you want to call it like that) along with it, already planned.