the problem is, MOS' next villian would have to be another powerhouse. if doomdays showed up on earth as a kryptonian killer, how does superman get away with a battle but we never see the other heros of earth? therefore, you have to introduce the other characters now. the world engine should have drawn them (esp the powerhouse ones like wonder woman, shazam (the rock), etc) out in the first movie but they got away with that. and no one wants to see Superman vs Lex Luther again.
The point is to use TDKR, an Elseworld tale to bring Superman and Batman together is the wrong approach. It's a big problem right off before we even get to the casting of Affleck.
See, these Hollywood studio heads and producers live in a bubble. They know him, see him about town, at parties, etc.
They think the public likes Affleck. They don't.
But their egos won't let them admit it was a blunder. They won't cut their loses. They just trudge straight ahead.
This is a guy who won the Razzie for playing Daredevil for cryin' out loud. He can't play Batman.
And don't forget that there was a time long before Disney bought Marvel that WB had the chance to make a JLA movie.
The director of the Mad Max trilogy, George Miller, wanted to do it. WB turned him down flat. They said it was too tough to pull off, too costly. Also, the rumor that Nolan didn't want Bale being put in the film was out there.
Then Disney developed their three phases project and the rest was history. WB was caught with their pants down.
Their Aquaman pilot (Mercy Reef) wasn't picked up.
Their Wonder Woman pilot wasn't picked up.
Green Lantern bombed.
Man of Steel underperformed.
...And here we are.
The problem is that they're still doing it wrong.