I believe this will be the last Dream World area with Unova Pokemon in it since I reckon Litwick will be an event. The Unova Starters don't have Overworld sprites so they won't be getting a DW event anytime soon.
I think that spread out through Dream World, Dream Radar and Hidden Grottos, all the Hidden abilities besides Legendaries and Starters have been released. Except Litwick line and Larvesta line. And some Male only events like Shadow Tag Gothita. (We have the evolutions though). And Litwick is the only one of those that has an overworld sprite too.
If anything, I'd love to see an area with just the Gen 1 to 4 starters in it. And throw in Pikachu for the heck of it. Even if it's for a limited time.
Baton Passing Speed Boost Blaziken! Oh god. That'll be a nightmare...