Couldn't see this anywhere else, but in an interview with rolling stone: "Slash, speaking on tribute games Guitar Hero: Metallica and Aerosmith, said to Rolling Stone: "Those are two ones that I think gives it some credibility. And they're doing a Hendrix one, which is great.""
Dunno myself, it would be awesome, but is he the most reliable source? Article here.

He isn't a reliable source and with the Hendrix family trust unable to get all of Hendrix's songs together and buy out all of the contracts that he signed his life away to I would really be surprised if Activision can manage it - though if they do they will find themselves with yet another guitar hero player.