I wouldn't care about big names unless it was remade as a movie. Honestly, I'd be happy to see it done by the local repertory theater company. Unless the play was filmed while it was on Broadway or at the Old Vic or whatever, I probably wouldn't see it with someone like Tom Hiddleston. I think David Tennant might be just about the right though. John was played by David Lee Smith, who was 44 at the time. Tennant is 53, but looks younger. Basically the guy needs to look old enough to be an established professor but young enough to still be attractive to grad students.

Incidentally, it was written by Jerome Bixby, who also wrote four TOS Star Trek episodes, including the famous mirror universe episode. That was the initial draw to me. That and John Billingsley from Star Trek: Enterprise. What can I say, I'm a sucker for Trekkie bait.