The most notable absences IMO
* Julius the Cat, and any character predating him. It seems Disney might want to distance themselves from their very earliest stuff. At least he’s been mentioned at DCA. Alice herself was briefly seen animated a few times in the shorts so could have technically also been used, as could Jack and Susie. The Laugh-o-Grams predate the Disney studio per se, but were still Walt’s creations.
* More “Silly Symphonies” characters, notably Bucky Bug, Little Hiawatha, and (the) Toby Tortoise & Max (the) Hare. Those characters were quite popular for their time and got crossover appearances from the 30s-70s, sometimes even their own comics. It could have also been funny to have King Midas show up, and there are some other historically notable Symphonies that are missing.
* The Br’ers, obviously. Same goes for the So Dear To My Heart roster, but I think even if the Br’ers are taboo someone like Mr. Bluebird could have been included instead. Ditto for World War 2 stuff, though there may be even more reason to exclude those. For that matter, we have nothing from Victory Through Air Power, nor stuff like Servant’s Entrance or Hollywood Party that Disney did animation for prior to Snow White.
* Someone from the Disneyland/Walt Disney Presents TV series like the Martian Robot. Yes, WDAS did the animation for that series as well, doing animation for a bunch of segments that got occasional use in crossovers like DTV but is nowadays almost totally forgotten. Ludwig seems to be the only representative of this meta series.
* Professor Owl. He was everywhere in the 80s and even had recent merchandise.
* Jenny Foxworth. How do you miss one of the female leads of your films?
* King Triton. How could you miss him?
* Mufasa. Probably the biggest absence in the entire thing.
* Merida, yes she is a Pixar character but she technically has been a WDAS character in a somewhat prominent role, so she could be included on that principle (but she’d have to wear her clothes from that film too). To a lesser extent, Kermit, Groot, Buzz Lightyear, Rocket Raccoon, and some Stormtroopers can technically show up but their roles weren’t as big as Merida’s. Splodyhead also cameoed in BH6. Sadly, we’ve never had cameos in WDAS stuff of the likes of Jack Skellington…
* Representatives of their 1980s-1990s shorts that are generally lost to time. There’s also the 1970s educational stuff though I’m not sure how involved WDAS were.
* Fantasia 2006 component short characters. I wonder if the whole thing rubbed off badly on them.
* Roger Rabbit’s shorts were done by WDAS, so he technically could have shown up.
* The Backson from Winnie the Pooh 2011, basically the only unique character in that film. That film is not considered part of the canon in some countries, but the same goes for DINOSAUR.
In an interview in the D23 magazine, they stated that the artists felt that if non-villainous characters who died in their films were included, it “didn’t feel right” to see them there, which would explain the lack of Mufasa. Regardless, Kerchak and Ray the Firefly make appearances despite them too dying, albeit at the end of their films.