Well, they released an In-Game map in the newest Magazine from Japan
The Pink stuff was me highlighting some of the new changes in B2W2.
First thing I wanna point out is the two Pink Circles connected by the Pink line. On the actual map, those circles are connected by a faint dotted line. For me that is one of the possible locations for that under water tunnel. The other possible location is the Pink circle near Undella where the Route line goes out into the ocean.
The Mountain with the Airplane from the large map is a selectable location as well. I have no idea what's going to be there. There is a small spot that looks like its in the mountains...I'm thinking that's a new E4 Route and Castle. I dunno why I think that but it just seems like that to me.
Do want to point out the lack of Ice which I believe confirms that the region isn't frozen (except for Chargestone Cave and Mistralon Cave cause they still look bluer in the game map)
Also just noticed there is another dotted line that goes from Driftvell to Iccirus. Those dotted lines can very well be underground routes.
I am curious as to what happened to Abyssal Ruins now seeing as the new Route over the water is right over where the Ruins should have been and I don't see a green blip to signify a dungeon/cave thing for it.