So IOTL, Walter was named after the first puppet Jason Segel owned. I'm starting to think his name would be affected ITTL, given his counterpart debuted six years earlier than IOTL and I gave him his OTL name (and performer) in my Muppet Quiz and Good Muppet Morning! posts. Ditto for Wendy, given her name starts with the same initial.
Maybe something like Dick and Jane, a nod to two characters from those old 1930s children's stories? (Though people definitely don't think of "Dick" as a person's name anymore.) Other options: Martin and Marcie, Jason and Janey (a wink to Segel), Peter and Patty, Charles and Cheryl, or just sticking with Walter and Wendy.
(I could go back and retcon his and Wendy's names in my Muppet Quiz and Good Muppet Morning! posts if I end up changing them. I might also consider giving Walter's Hensonverse counterpart a different performer, like Joey Mazzarino, who auditioned for Walter IOTL, Dan Garza, or John Tartaglia. Might be a little late though.)
EDIT: Shockeye and I agreed to name them Alvin and Audrey. We're still working on Alvin's performer, though Karen Prell will still do Audrey. The Alvin name would really lend itself well to, say, a one-time instance of Piggy yelling his name in frustration as a homage to how Dave Seville yells that name to the chipmunk. I'll edit my guest posts once Alvin's performer is decided on.
EDIT 2: We decided on Artie Esposito as Alvin's performer. Artie wouldn't need to understudy for Kermit when Disney would stick to the principles of not having fill-in performers when the regular performers are still active and thus ruining the Muppets' integrity.