[RogerBW]

Apart from John's characters mentioned above, the ones in my file are one musician-conductor from the 1960s psi campaign (who got sonokinesis of course), and two actors, one of whom also has Fight Choreography.

I don't think these skills have ever been particularly important in my games, though I've always rather fancied Steffan O'Sullivan's pet campaign idea from Swashbucklers of the roving Commedia dell'Arte troupe.

I think that specialising a required specialty is basically too fiddly for GURPS: the closest we get is Hyper-Specialization (Power-Ups 2, p. 16) which is too narrow to apply here. I suspect that if I were to model a casting specialist I'd just call it Group Performance (Casting) and allow a small default from Directing.