Another name you could throw into the hat would be Robert Llewelyn.
Hey, he could even morph into Kryten from Red Dwarf in the futuristic zone.
I hope they revive the Computer and of course a Mumsy character. That position was sorely missed after O'Brien's departure.
If you really wanted to go down the Richard O'Brien route, someone like Jason Bradbury would be a good shout, although I don't think he has any acting experience as such.