I'd love that parade a lot more than anything now, but I have to be realistic. Average guests wouldn't know who the characters on the parade are... Unfortunately, it's probably going to be filled with characters from the 2000s until now, with some classics mixed in.
Unfortunately you're going to get something that involves Cars and Frozen. Love your idea of the tribute from each decade but a majority of people won't know or care about those movies.
You'd be surprised at how home video keeps even the rare characters in the public conscious. The Aristocats and Rescuers might not be A-list stars, but many children are familiar with them; and why shouldn't Disney use its massive theme park merchandising machine to re-introduce the classics?
The decades offer plenty of recognizable characters. Here's a quick list off the top of my head:
20s — Mickey, Minnie, Pete, Oswald (a pipe dream at WDW)
30s — Pluto, Goofy, Donald, Daisy, Snow White and the Seven Dwarfs, Three Little Pigs
40s — Pinocchio, Fantasia, Bambi, Dumbo, Chip and Dale, and throw in the Headless Horseman/Ichabod Crane for a thrill. Brer Rabbit/Bear/Fox could slide in as a generic riverboat theme.
50s — Peter Pan, Alice in Wonderland, Cinderella, Sleeping Beauty, Davy Crockett
60s — Winnie the Pooh, 101 Dalmatians, Jungle Book, Herbie the Love Bug, toss in Sword in the Stone to please fanboys. Add POTC and HM for theme park synergy.
70s — Robin Hood, Aristocats, The Rescuers, Pete's Dragon. Admittedly weak. Parade producers would have to toss in a lot of dancers to make up for this unit.
80s — The Little Mermaid, Roger Rabbit, Ducktails. Let's be honest and admit "Fox and the Hound" and "Great Mouse Detective" would never make it to a parade. Break park boundaries and add Figment to the 80s unit.
90s — Beauty and the Beast, Aladdin, the Lion King, Toy Story. If needed, Pocahontas, Hercules, A Bug's Life, and Hunchback could fill empty holes.
2000s — For Disney, this era was just as weak as the 70s, but Pixar easily wins this decade. Nemo, the Incredibles, Monsters Inc, Cars. Maybe add Princess and the Frog, but that movie doesn't fit the overall flavor from this parade unit.
2010s — Tangled, Frozen, Big Hero 6. Wreck-It Ralph has, unfortunately, proven to be as ultimately forgettable as some of Disney's lesser films from the 70s and late 90s.
The point is, Disney could easily fill a parade with characters from across the decades. But since characters are usually grouped by themes and not time periods, this parade will probably never happen.