So, a game that has songs that are only in 4/4, with a guitar that plays only fifth chords and a bass that plays only the root note of whatever the guitar is playing. Yawn.
Just because
somerandomguy76 said:
It think there's just as much chance of that as somebody making
Ska Band 
Some genres just don't lend themselves as well to video game format unfortunately.
Not that
Ska Band wouldn't be awesome...
I like ska, but it would also be boring on GH/RB. While the bass line is usually good, the drums would be far too easy and the guitar would just consist of playing one chord on the offbeat.
Iron Mal said:
What about a Jazz Hero?
Blues Band?
Classical Hero?
Now there's something interesting. Jazz and Blues would make great additions (I'm leaning more towards blues). Classical Hero would be difficult to implement, though. Very few Classical* compositions would work, unless we get new instruments (a flute, a cello/violin and that big drum they used). Plus, how many people can sing The Magical Flute or Nessun Dorma?
* I'm using Classical in the colloquial meaning, which indiscriminately lumps every period of non-contemporary music in the same pile.