Here's an idea down the line, either as a playset or as a downloadable addition to the game... a Super Vault and/or Mass-compatible Playset.
If you've not heard, Incredibles (and believed to be others) have a character vault, the idea is simple, you get ALL the characters and you can unlock the vault for Toy box goodies (exact contents unconfirmed).
So... what if there was a Super Vault, unlocked only when you had a whole series of characters? Or perhaps a vault containing vaults, one for each season or set release of characters? Updated by downloaded content updates.
Likewise... a playset which supports the use of ALL characters available, and such gameplay as to require you to switch your characters in game to deal with the challenges/enemies thrown at you?
Obviously, to avoid the issue of the person not having the required character, it would have to be "character types" or provide multiple "paths" to go, so if you don't have that character, you could use a different one and progress a different path (leaving you to wonder what it would be like to play again after you get that character).
There could be "open choice" sections, where you don't have to have a specific character, or type of character and it's up to you to chose the best or your preferred character to use.
Granted, I know what you're going to say... Toy Box and Toy Box Adventures... but what I'm thinking is more of a collision of playsets, a story, but maybe we can replicate it in Toy Box.. I'm just worried about the "memory limit" and how we can tailor things to characters in Toy Box.