I admit that I have not read all the replies to this question, but I do think there is room for Walter along side Scotter and Rowlf. First of all it is three different puppeteers, so they all could appear in the same scene. I admit there are similarities between Walter and Scooter, but Scooter has been around longer, and for those visiting the forums who have not done theater as an actor or tech or as anything really, the stage manager runs the show. That seems to be the role Scooter has evolved into. Sure he still wants to be on stage, but Kermit could not run the show without him. Walter could fill in, but he is in no way seasoned. As far as replacing Rowlf until Walter plays a piano Rowlf is secure. And even when/if he does the Rowlf is secure.