In a Rolling Stone interview, former Guns N' Roses guitarist Slash was asked about his involvement in Guitar Hero when he said:

And they’re doing a Hendrix one, which is great.

Although I doubt Slash is privy to Activision's longer term Guitar Hero plans, this sounds plausible for a couple of reasons. Neversoft has a clear bent towards classic rock, as you can see in the song list for Guitar Hero: World Tour. Furthermore, when I interviewed Neversoft director Brian Bright recently, he told me by far the biggest licensing hassle was dealing with the Hendrix estate. Could part of that hassle be that the lawyers have been busy with more than just the rights for the two Hendrix songs included in World Tour?

Thanks to Shack News for finding this one.