Guys, we've been over this. Epcar is voicing the Joker in this.
- You can faintly hear him in the "Lines Redrawn" trailer.
- He has hinted at the Joker role in I2 on twitter.
- He has said on twitter last year on March that he was about to do some recording for Joker. To my knowledge, he isn't voicing the Joker in anything other than I2, so unless there's some secret project we don't know about, it's him.
I love Hamill as much as the next guy, but at best, he's going to be a premier skin voice for the Arkham games. Besides, I... kinda like Epcar's Joker. Sue me!
EDIT: Also worth noting, there's at least 30 min. worth of voice dialogue for every character just from opening match interactions and clashes alone. If Hamill did voice Joker here, it'd be a BIG commitment. Not Arkham Knight big, but still pretty big. It wouldn't be a quick one and done type role.