Metzen said we would go to Ulduar for TLT. In the first concepts, Ulduar was supposed to be its own continent. What if, instead of a completely new Northrend, TLT took place in a completely new land?
What intrigues me is that he said that for Midnight we'd be going to Quel'Thalas, which is a region that already exists and can be developed further. However, he did specify Ulduar for TLT, not the Storm Peaks, which is where the raid is set.
It's possible that Ulduar will be its own new zone, possibly including the Storm Peaks and brand-new regions.