Well there really is no one at this point that Royce really matches up well with, atleast someone that is a marquee fighter. For his final fight it would be stupid to match him up with a nobody and they couldn't give him a contender because they would smash him. I know when he fought Hughes it was at a catchweight of 175lbs. so he probably could fight at 185lbs too.
So between all the Welterweights and Middleweights, Damian Maia is about the only person I could see matching him up with. Maia's standup is pretty horrible but so is Royce's. It would end up being a grappling clinic but fuck it, the people of Rio would eat that shit up.