I think Khan would be too big for Mitchell. Even at lightweight Amir was massive, and Kevin's only just stepped out of the super-feathers. I like Kevin, but I think Khan would be too big and too fast. It's one thing stepping up to fight bigger guys if you can retain an advantage in speed and agility, however it's much harder if the guy's not only bigger than you, but faster as well.
Mitchell offers Khan nothing... The only way this fight will happen is if it goes belly up with GBP... I think that the handspeed of Khan will be far to much for Mitchell.