Future PS All-Stars characters?
First off, let's assume every character from the first one is returning (except for Dante who is replaced by DMC5 Dante, and also Kratos from GOW3 is replaced by Kratos in the most recent God of War.)
I have a few ideas in mind on who could be added though:
Rayman
Crash Bandicoot
Lara Croft (Tomb Raider)
Spyro the Dragon
A Patapon (preferably a Hero Patapon from 2 & 3, but any would be cool.)
Dart (Legend of Dragoon)
The Hunter (Bloodborne)
Aloy (Horizon Zero Dawn)
Delsin Rowe (inFAMOUS: Second Son)
Croc
Gex
Gabriel Logan (Syphon Filter)
Knack
Alundra
Wander (Shadow of the Colossus)
The Protagonist (Soul Sacrifice)
Alucard (Castlevania, and yes I know he appeared as an assist trophy but he'd be more fitting as a full character in this game anyway.)
The Messenger (Tearaway)
Chris Redfield (Resident Evil)
Kazuma Kiryu (Yakuza)
Klonoa
Villains:
Dr. Neo Cortex (Crash Bandicoot)
Ripto (Spyro)
Mr. Dark (Rayman)
Lloyd (Legend of Dragoon)
Vergil (DMC5)
Albert Wesker (Resident Evil)
Dr. Nefarious (Ratchet & Clank)
Wendigo (Until Dawn)
Old King Allant (Demon's Souls)
Potential Bosses:
Dodonga (Patapon)
Gaius, The 3rd Collosi (Shadow of the Colossus)
Metal Gear RAY (Metal Gear)