Lesnar did the job to Kurt Angle in Japan on June 29th 07 which was after his MMA debut. I'm just saying if he got offered a 7 figure number for one days work he'd likely consider it, most people would. He's said he didn't hate pro wrestling, he hated the road, which he wouldn't have to go on for this.
However as mentioned a million times Dana White would have to approve it and he's not going to.