1) It's not "Rock Band 4"
2) It's not "Rock Band: [artist]"
3) It doesn't add any new peripherals
4) It's not limited to the XBox, and might even include a Facebook version. This is the real wild card, is it really a game so simple that a full version can run on Facebook? Or does it just have Facebook "integration"? The one article that mentioned the Facebook connection has never been clarified, officially, as far as I can tell.
5) Rock Band fans specifically are expected to be excited about this title (as opposed to Dance Central fans)
Does that mean it's a Rock Band title? Not necessarily. Consistant with most of these facts [except the Facebook part] is the idea that it might be some sort of spin-off to RB3 (i.e., same engine, same instruments, but includes new songs and / or game features like quests for your band). That would be the most awesome thing I could hope for, realistically. It might be something much more radically different. A new rhythm game altogether? Will it use RB instruments, and RB DLC? We don't know! The torture continues, until Tuesday, or maybe Wednesday.