Given the fact that BDSP was a failure to a lot of people, I hope we get a full 3d world for BWBW2. I don't know how they will combine the games, but it is something I would love to see. Unova is my favorite generation and the generation that stopped me from losing interest in pokemon during 4th Gen when it was announced. I would hope they would change it up a little bit though and actually explain the giant tree at the center of the region that never got an explanation. And they would have to do something with Dream World.
If they didn't make Unova again, it be the only region without a 3D game. And it was made for 3D in mind. If the 3DS can handle cutscenes like what Detective Pikachu had, they should be able to give Unova justice.