Matt Damon as the Joker
or Casey Affleck
No and NO.
Much as Damon is a very good actor I don't think he suits playing Clown Prince of Crime.
If anything Casey Affleck should play Riddler or Gotham PD officer. Thsts just my opinion.
Casey Affleck could play John Blake.
Nic Cage would be glorious as the Joker. or the Penguin. Or Killer Croc. Or even Catwoman I'm sure.