Having been on the show in the FCX Clarity episode and for SIARPC, I think it can be said that he has been interviewed enough. Should they want to review one of his toys (which seems doubtful at this point) he could make another appearance then, but it is my opinion that SIARPC should really be reserved for those who haven't been interviewed on SIARPC.
They've had Ken Block on twice outside a SIARPC context.
Also, if he or Tanner appeared and did a lap, what board would they go on? They can't on the normal board; they're racing drivers. But they can't go on the F1 board either; they're rally drivers. It's either expand the F1 board to include other racing drivers, or start a new board for other racing drivers.