I don't think this is a new idea they've suddenly come up with, it was always going to be Joker.
By announcing it as Total Mayhem and then announcing the Joker has 'taken it over' you have twice as much publicity for no real outlay.
It's giving everyone a reason to talk about it again now.
Don't tell me Six Flags sat there and decided against comic book themeing it and then changed their minds again.