This is my inspiration for a great Idea.
As we travel through Unova for the second time, we expect to find a few new things along the way. The first game did not use HMs at all. What if ALL of the new areas of BW2 are right under our noses, but hidden by HM Moves. We didn't see them the first time around because we never used HMs.
Example: When you surf under Village Bridge, there would be a Dive Point added. This Dive Point goes to a tunnel, which goes to a Brand New Cave to explore and enjoy - and to met rare and exotic Pokemon!