My immediate thought would be a Travis Barker led supergroup, with say Liz Rodriguez doing vocals or something. Barker is pretty involved in rap already, he's layed drums on the Game's tracks and he has some sick remixes like the one of Em's 3 AM. He was a member of a rap-influenced band called the Transplants and another called Expensive Taste with Paul Wall and Skinhead Rob, Transplants had some good stuff, ET is OK. Also, him and Yelawolf would look badass standing next to each other, with the similar hair and tats.
My idea: A group with Barker on drums, Liz and Yelawolf singing (he can sing), someone else on guitar, and Em throwing in some production for tracks that have that rock/rap feel like Lose Yourself. I'm getting my own hopes up...

Then again this could be a terrible idea and end up sounding awful and being Em's Rebirth. Who knows...