MSWORD talks about Walter separately, so I don't think it's him (or Constantine) that is the "one important character palisades never made" being referred to. To me that could imply that it's a character that existed during palisades' run but they didn't do.
He mentions Sal is not who he is talking about, so the Monkey is out of the guessing pool for series one.
Uncle Deadly & Sweatums were made as figures by Palisades, so they are out. He also mentions Vet's Hospital for his wish list, so Dr. Bob and crew can be removed from guessing.
He also doesn't say "version of character"...just "character", so different outfits (like Dr. Bob again) would be excluded.
Maybe J.P. Grosse? Add him to my guesses along with Thog, Nigel, & Mahna Mahna.
Bobo is a good guess too, but I personally wouldn't launch the line with both Fozzie the bear and Bobo the Bear in the same small wave.