I doubt it.
Firstly, if there was going to be two regions in a Pokémon game, I am willing to bet the money I'm saving for a 3DS that they wouldn't make two entirely new regions for the sake of it. There'd be no point.
The whole "returning to past regions" was a trait that I loved in GSC/HGSS, but it's something that will remain exclusive to GSC/HGSS, I think it's safe to say at this stage. Normally saying something like that would depress me, but because B2W2 had the World Tournament, I'm feeling a lot better about a whole new adventure.
With that said, someone brought up the fact that BW was a reboot, we could consider this as the "GSC" to BW. I think that's out the window because of B2W2 though.