Surely people were saying things like this when The Avengers were first announced.
If a JL film will be done (and I'm I've read that it has a script, though knowing film studios that can easily be stuck in development hell) it has to be darker than The Avengers as that is kinda the tone the films have taken. A little more serious. Even Green Lantern by far the lightest recent DC JL character film is still a little darker than some Marvel outings.
Question is - is there anyone with the skill who can put all these big characters in a single film and make it (kinda) serious without the audience going "oh come on, lighten up"?
Who ever decided to go with Joss Whedon for The Avengers deserves a significant raise cause honestly IMO for the films Marvel had established he was my only choice for it, literally, I posted that on a few forums as well

. I can't however think of anyone who would be able to do it for the DC characters though.
Nolan - My favourite Director but just can not handle a big full of so many big characters. As much as I love Inception and TDKR that was a big issue.
Affleck - Okay a reasonable choice I guess but that is way WAY out of the guys comfort zone so far. Plus he has already turned it down.
Kevin Smith - Yes this is a name I have seen elsewhere. He can write dialogue and is a HUGE self-confessed fan of comics (mainly Batman) but he himself has said he has turned down films like this in the past and is also quitting filmmaking. I like the guy and I very much enjoy his films and podcasts but this would set off alarm bells.
J.J. Abrams - Cause his name seems to be atatched to every film and TV show these days
But other than those, and some others whose names escape me currently I can't see anyone for WB to pick who isn't from out of the blue. At least Whedon had ventured into action films and was well established to be able to deal with big casts.