Whirlwind as Juggernaut could have been really cool. They could very easily mash those classic costumes up in a way that pays tribute to both characters. Their powers would also play off of one another.
@frozen: you forgot that this is fiction. It is not Realism. That is beauty of comicbook. People often forget about that
No, no one has forgotten that comics are fantasy. There are tons of supernatural characters. What sets the Batman/Joker relationship apart and makes it so poetic is that Batman could kill Joker at any point and end all the suffering and murder by ending one mortal life-- but due to his unshakable code of ethics, his one uncrossable line in the sand, he won't. That fact also makes Joker unwilling to actually finish off Batman, gaining too much amusement or always trying to get him to cross the line -- and thus they're stuck in this neverending dance, with a trail of bodies at their feet. It's self-defeating, but nearly inevitable.
It's not about realism.
Making Joker actually supernatural, especially if it's retroactive, cheapens the relationship.
It's clearly tied to their cinematic decisions and restrictions.
It'd make no sense if they weren't mutants, though, given the events post-M-Day.
Quicksilver was depowered, and got wonky powers via the Terrigen Mists. Especially if he'd already been an inhuman, this just seems off.
If they want the twins to not be Magneto's kids, I don't know but there COULD be a decent story there. Making them not mutants seems forced at this point. But then, it's not like continuity following Magneto and company has ever been intelligible.
Not to say it was all that great, but I'm surprised that Sin City: A Dame to Kill for wasn't in the running. It was certainly better than the RoboCop remake and Transformers 4, at the very least, and was based on a pretty well loved comic.