Re: Should this have a Batman Villian and if so who should it be?
I think it's way too soon for Joker. It's only been 5 years since the last one, 7 by the time the movie comes out.
Joker would crowd the film and put too much focus on the Batman side of things. Other bat rogues deserve a shot before Joker ever makes another appearance.
There was 19 years between Nicholson and Ledger and im not saying you have to wait that long next time but that kind of wait really helped. TDK was out in 2008, so I would give it til the early part of the 2020's for the next Joker appearance. Referencing him through dialogue or hearing a maniacal laugh in the halls of Arkham is fine, but physically we shouldn't see him for a while.
Let them do this Batman vs Superman and eventually a Justice League. At some point at the end of this decade let them pump out a solo batman movie with a villain or two that Nolan didn't use. No Joker yet.