When Tyson reffed the WCFC a few months back he said that there was no way he'd step into the ring/cage with these guys (mma fighters).
He knows that these are professional fighters & not a throwback to the UFC1 days when boxers fought Joe Son Do artists (still laugh at that!). Also his refereeing showed that he had little knowledge of mma, so I can't see him ever fighting at mma.
I've said it before, but it still amazes me that people bring up retired boxers names when talking of potential mma fighters. The sports are chalk & cheese, you may as well ask when Dennis Rodman is gonna make his mma debut.