On the live letter X test there's this one BGM that sticks out from all the rest:

http://youtu.be/4pK1kjVtI_g ( Skip to 1:57)

Either it's a replacement BGM for some area, or there's going to be a zone in the open world somewhere. It doesn't sound very "Housing" like, They already revealed the Beastman Tribe BGM in the 10 min trailer.

I am very curious as to where this BGM falls into 2.1, it sounds Open world I can tell ya that.