Lylle Breier has responded to my email (and to emails from other fans) with the following statement:
We also absolutely appreciate constructive criticism, which brings me to your comments about Kermit. I can assure you that if we ever decide to substitute a performer, we do not do so lightly or arbitrarily, only after careful consideration. Beyond that, however, I hope you can understand that we are not in a position to discuss our private business dealings with any performer.