In Gen V, I've noted that Plasma Gang has been seen in nearly every area, through out the story.
Also, you fight your rivals more often, and after beating one, the other one follows really soon (ex: If you leave Hiun City, Beru will fight you, and as soon as you enter Route 4 (the dessert), Cheren will fight you).
But I really love the Isshu Region's areas, but it would been better if Plasma Gang wasn't around that often, I mean, they're even at the Pokémon League.