Could happen. Mitrione called Jackson out today, and Jackson accepted. They could fight at a catch-weight, making it easier for Jackson to get out of the UFC. Mitrione has a fight scheduled for UFC 155 but it is against Phil de Fries and isn't as marquee as one with Jackson would be. Jackson is currently nursing an injury that kept him out of UFC 153 in Brazil. Mitrione fights at 255-lbs. meaning he'd need to cut at least 25-lbs. to meet Jackson at 230, which is about half-way. Sounds unlikely. According to former UFC heavyweight Sean McCorkle, a member of Jackson's entourage made a comment to Mitrione's Asian wife a few weeks ago at a club that has Mitrione incensed. Mitrione and Jackson first crossed paths on the set of The Ultimate Fighter 10, where Mitrione competed on the opposing team coached by Rashad Evans.
Rampage has offered a "winner take all" fight where all purses and show money and endorsements/bonuses would go to the winner. Mitrione wasn't jumping at the chance to accept the offer.
Of course Rampage would offer that. He's a multi-millionaire. I imagine Mitrione lives fight to fight. Either way, I'd love to see this fight. Why give Rampage anyone meaningful to fight if he's bolting the UFC after his next fight? Give him a slugfest that he wants.