I had an idea for a DJ Hero way back in 2006. I'm not sure if the actual game is going to be anything like my idea, and in all likelyhood it's going to suck, but it sounds kinda cool.
In case anyone's wondering, my idea would basically be that you're a DJ who plays at various events, and are gven free reign to do whatever with the material you have. Like a real DJ, you'd have to react to the crowd's desires - whether the tempo should be slow or fast, what genre, etc, and failure to meet them would lower your crowd rating. You'd lay down tracks in real time on this sort of simplified hybrid DJ station using pre-selected songs to sample from. If you do well enough with a certain artist's material, then you're given access to the multitracks of that song, allowing you more versatility. And every now and then, there'd be boss battles against real-life DJs of various genres that specialize in fields like scratching, mixing, etc.