I've been watching this show since the beginning. I think I've seen every episode.There was an episode this season where the Top 5 list was the Top 5 stars they'd like to have on "That Metal Show" but haven't been on the show yet. If I remember correctly, Eddie Van Halen was ranked #1.
Some other people mentioned on their wish lists were Ozzy Osbourne, Gene Simmons, Paul Stanley, James Hetfield, Steven Tyler and David Lee Roth. If you think about it, they've interviewed pretty much every major hard rock/metal star who was alive in the years that the show has been on the air. I think their biggest "get" was Axl Rose, but it was kind of a dumb, uninformative interview because they seemed intimidated by him and he probably demanded to see their questions before he agreed to do the interview. Axl's interview with Jimmy Kimmel was better.