-There's a big hole to dig themselves out of. Too many of DC's properties are tied with Warner Brothers in a way that leaves them just the indentured servants, working as consultants and whatnot.
-Even after they find a way out of that, they still have to start tying these characters together. Even if Christopher Nolan and Christian Bale wanted to do more Batman (which they don't), it's very unlikely that his gritty, semi-realistic style of storytelling would gel well enough that his Batman could exist in a larger superpowered community. Then again, Hawkeye exists in the Avengers, so you never know.
-The Superman franchise is still looking for forgivness. Don't get me wrong. I have complete faith in Zak Snyder's directing skills (despite wack ass Sucker Punch), but it's going to take a lot to get the taste of Superman Returns out of our mouths. You know...like maybe Superman could actually punch a bad guy at some point.
-Nobody really knows what the hell is happening with the Wonder Woman project. That makes three of your top characters that need a fresh reboot even though I don't think Batman and Superman need origin stories at this point. You would have to look far and wide for someone who doesn't know that Superman is from another planet and Batman's parents were killed when he was a kid.
-Even after you establish a contained cinematic universe for all these characters (I'd go with a Flash movie to start), it would take amnesia, an alien invasion and Oprah giving away coupons for massage parlor happy endings to make people forget that Green Lantern was easily one of the worse cinematic superhero experiences to occur in the past five years.
I'm not saying it won't ever happen, but it'll be five years at the very least!
