Pretty simple, but with Sony Santa Monica taking over DLC, I'm really hoping for many more characters to be released. Who are you holding out hope for? One thing I'd like to see are rivals released. Like a standalone villain opposite their protagonist, just like what they're doing with Zeus for Kratos. I'd also like to see how obscure Sony can go to really highlight some characters.
Crash Bandicoot (Crash Bandicoot series)
Dr. N Cortex (Crash Bandicoot series)
Spyro the Dragon (Spyro the Dragon/Skylanders series)
Tomba (Tomba series)
Cloud Strife* (Final Fantasy VII)
Sephiroth* (Final Fantasy VII)
Lazarevic (Uncharted series)
Clank Standalone (Ratchet and Clank series)
Nefarious (Ratchet and Clank series)
Captain Qwark (Ratchet and Clank series)
Daxter Standalone (Jak and Daxter series)
Kor (Jak and Daxter series)
Panda King** (Sly Cooper Series)
Calypso (Twisted Metal Series)
Musashi (Brave Fencer Musashi series)
*I understand there's Dissidia, and I have other personal FF favorites I'd rather see, but from a "Playstation All-Star" point of view, Cloud/Sephiroth fits best due to his marketability
**It's hard to pinpoint one Sly Villain as they're all memorable/similar. I felt Panda translated really well.
I didn't go into detail on movesets or anything, but I'd love to hear some ideas of your own. And if you have a moveset or any Supers in mind (like Crash wearing an Aku Aku mask for one hit kills) I'd love to hear them.