Here are a few characters I'd like to see return:
The Two-Headed Monster
I'd like to see Joey Mazzarino and Jerry Nelson (or at least with David Rudman, Baby Bear's performer) return to perform the Two-Headed Monster again. We haven't heard from them after Journey to Ernie was taken off, and Joey is a suitable successor to the late Richard Hunt.
The Amazing Mumford
For those too young to remember, he was the inept magician who whose tricks would never come out right. If Jerry is unable to perform Mumford due to his age and COPD, maybe he could just
voice him instead.
Ruby
This curious tomboy was one character that came up during the "neo-old school" period from 1988 to 1992, when there were several new (and short-lived) characters introduced. Ruby is severely underdeveloped like most of them, and if Camille Bonora can't play her again, maybe Leslie Cararra or Stephanie D'Abruzzo would be fitting substitutes.
Benny Rabbit
Perhaps one of Kevin Clash's best (and grumpiest!) characters, he would make a great sidekick for Oscar.
Oh, and Snuffy, Big Bird, Grover, and Oscar are still around; they're just underused due to there being so few episodes each season nowadays (26 compared to 130 several years past). And I don't mind Abby Cadabby. I
do mind that producers are forcing her into the show every chance they get just like they did with Elmo and Zoe.