I know it's a stretch, but a character creator in All-Stars could continue Sony's push of Play Create Share.
Move sets might be tricky and character types and options would have to be expansive. However, this would give fans the appeal to create their own experience with the game.
Additionally, Superbot could potentially hold a contest to feature the winning character in a future platforming game. Of course, one entry per person would have to be enforced with the option to buy extra entries.
Personally, I believe a 2D pixelated Cole MacGrath on acid would provide Sony with an excellent "less floaty" AAA 2D platforming experience. However, this would be an excellent opportunity to push the idea of new character development while giving fans an opportunity to work with an established gaming studio.
You're right. They have to keep making licensed characters. I'd like to see at least 10 more, but this would be a good idea once the game is already established. Let's face it, the more DLC, they make for this game, the more people are going to buy it. If you add Cloud Strife, you attract different fans than if you were to add Leon Kennedy.
It would take a lot of time and resources. I thought of this idea while thinking of something to do with Demons Souls in DLC form. One thing out of a whole lot of things the Souls series does really well is it has an excellent character creator.. so if you were to make something that complex, it could work.. and if All Stars has sold 5 million+ copies in a year and added 10-15 characters.. which is conceivable, I think Superbot could get clearance for some heavier DLC.. new modes and all. I wouldn't mind seeing the option to (someday) be able to adjust the gravity settings and be able to knock people off the screen.. but that would have to be AFTER the game is established and people know that it's not just a SSB clone.