kinda like the idea that the real joker is somewhere out there still, it creates this aura of mystery around the character, almost as if he is out there in the real world waiting to reveal himself. Makes him all the more terrifying
also liking the idea of the flash being from the future to warn the justice league, it gives him a good reason to be part of the team and differentiates his character and makes him edgier. I like how they're putting things together and the team members all have their own individual reasons and circumstances to come together as a team.
I also predict that superman will die or appear to die at the end of bvs at the hands of doomsday, superman will sacrifice himself as a last resort and both he and doomsday will die and return in a future film, this will be his way of making amends for the destruction caused by his fight with zod in mos and return him to the status of an iconic hero to fans who were dissapointed in mos.
Superman will return during the last 3rd of justice league, this works fine since you still have batman, ww, flash, aquaman, cyborg to carry the first half of the film. When all hope seems lost for the league superman will return and fly near the sun to power up and then proceed to unleash an epic beatdown on the villian who is most likely to be brainiac.