I don't know about directors for DMing... but I know what celebrities I would want in my game.
Christopher Walken: He'd play a Wizard or Sorcerer, always show up on time, bring his own dice, really get into character, but in crucial moments, instead of casting a key spell, he'd pull out his dagger and stab his opponent in the throat. He'd stay after the game to talk about the plot and story. He'd always spend like 10 minutes making kissy noises at my cat if she happened to come out during the game.
Snoop Dogg: He'd play a Rogue/Bard, and he'd always want a lot of henchmen. He'd show up on time to the game, but would always bring a few members of his "posse", one of which would roll his gold-plated dice for him. He'd break character sometimes, and his character would often get the party into a lot of trouble, but he'd help them all get bailed back out. He'd have to leave right after the game was over, probably to get back to the studio. I'd have to remind him I don't allow smoking in the house.
William Shatner: He'd play a Paladin, want to be the leader of the party, and always show up late to the game. He'd always ask to borrow someone else's dice. He'd REALLY get into character, and his character would make a lot of dramatic speeches and get into combats that the rest of the party would have to struggle to help win. He'd not only stay after the game, he'd crash on my couch after raiding my fridge. I'd have to keep his character sheet so as no mysterious "bonuses" appeared next game.
Ozzy Osbourne: He'd play a Cleric, even though everyone thought he'd play a Bard. He wouldn't show up for every game, and he'd only have a few dice, most of which look like they've been chewed on by dogs. Either he wouldn't get into character, or his character acts just like him. His character would forget to cast heal spells sometimes, and the rst of the group would have to wait a few minutes while he picked out which die to use in combat. He'd usually have to leave most games early, probably to tour or do his TV show. I'd have to go find him when he got lost while taking a bathroom break and was holding up the game.
That would just be hilarious. And fun. If they ever make a commerical for a roleplaying game, they should use a similar gimmick where celebrities show up at some regualr guy's house to game. I volunteer!