The group is called Prophets of Rage. It was never advertised or sold as a RATM reunion. It was a a mysterious rage related something until the cat came out of the bag.

And for all you smart, dumb niggas who say Chuck wouldn't be a good fit: https://www.youtube.com/watch?v=yQ_zUa4IFsw

Also, before Audioslave formed and Rick Rubin suggested Chris Cornell, Chuck D was the one they wanted to front the new incarnation of the band.