Would it be too much to ask for literally every property that Disney owns??
Short of that, here are some of my top ones with some other ideas as to how they could go about playsets, rather then restricting them to one film or franchise:
Classic Characters - Either a black and white playset as others have suggested, or an Epic Mickey esque one using the designs of Mickey and Oswald from those games. Mickey and Oswald would be main characters, with Minnie, Donald, Goofy, and others separately.
Pinocchio - so many great character opportunities! This would be a simple adventure game, where Pinocchio has to choose between right and wrong during his journeys. Characters could include Pinocchio, Geppetto, Foulfellow, Stromboli and others.
Peter Pan - I think this one is an obvious winner. Peter Pan is very popular with young boys, and many people have been asking for Capt Hook on Infinity's facebook already. Playset would focus on flying around Neverland and exploring, maybe finding the Lost Boys scattered around?
Disney Afternoon - Darkwing Duck, DuckTales, Gargoyles, Talespin... perfection.
Disney Princess - while ideally I'd love to see each film get it's own playset, I don't know if that's very realistic. I think one way they could get all those characters into the Infinity universe quicker would be by grouping them into larger franchises. For the Disney Princess playset, they could maybe make a single level in each of the princess's world. Snow White and Cinderella would come with the playset, with Aurora, Ariel, Belle, and all the rest available as well. After they made the princesses available, they could then maybe add full playsets for those that lend themselves to that, which would allow them to add secondary characters (and princes!). An Aladdin playset, Beauty and the Beast, Tangled, etc.
Walt Disney Classics - another grouping that would include some of the earlier films that don't really lend themselves to entire playsets. Dumbo, Bambi, Fantasia... maybe some characters from the shorts?
Disney Vault - this group would include characters that are seldom heard from - those less popular films. Robin Hood, Rescuers, Black Cauldron, Emporer's New Groove, Atlantis, etc. I could see this as a platformer with levels themed to each film.
I'd also like to see them finish off the rest of the Pixar films. Finding Nemo, although I don't how those characters would translate to the toy box. Bug's Life, Wall-E, Up, Ratatouille, Brave.
Also, I know it's impossible, but how cool would it be to see Harry Potter as part of all this? Yes please.