I wouldn't mind it at all, they are all top 5 caliber fighters, so why not. But I say no. Rockhold and Gil to a lesser extent aren't huge names for UFC only fans. If they bring them over and give them a favorable matchup they could get their UFC cred. But I wouldn't mind if any of them got a shot.
In order of who deserves it Melendez probably deserves it the most. Then Rockhold. Then Marquardt.
I would pick none of them vs. the current champ. Melendez would definatly give Bendo a good fight though. Actually that would be an awesome fight, but Benndo's kicks and cardio would be the difference.