From the MTV owned Country Music Television blog (and therefore very probably not empty conjecture!), the first real word of Rock Band branching out from its, well, rock roots with the first all-country DLC:
Just wait until Dec 16. That’s when Rock Band will add five country songs to its downloadable content for PlayStation3 and XBOX 360… This bundle’s going to have [Dierks Bentley], plus Brad Paisley, Brooks & Dunn, Miranda Lambert and the Dixie Chicks.
Say what you will about the tricky mashup of four spike-and-leather be-goth’d members working their way through a cover of my grandmother’s favorite hits, but more diversity is always a very good thing, especially if it spurs more back-catalog digging (‘Ring of Fire’ being a new Offworld hit in iNiS’s karaoke game Lips).