their is many problems with making a justice league movie first the fact that they already did along time ago which had flash, green lantern, atom, some fire girl and some ice girl, also it had Martian, manhunter.
which is not a success and a fear of repeating the failure is holding them back.
some other concerns about DC movies is how they plan to do this I have some movie release information I'd like to share
as far as I know a superman movie is coming in 2013 and a flash movie along with a green lantern movie is coming in 2014 a year before the justice league although others are saying that they are doing stand alone movies after the JLA movie which comes in 2015. maybe I'm wrong I got my info from http://www.movieinsider.com/movies/-/2014/
I think that its a good idea to use the man of steel, the flash, and the green lantern movie to set up the JLA.
anther problem is wonder woman and hawkgirl you see the problem is if you have a stand alone movie you don't know how much fans well show up and both are too famous to be in anther hero movie although hawkgirl can be in a hawkman movie. with wonder woman their stuck. that can lead to a problem. I think they should take it to a vote. to see who would see the movie. the only reason I say this is because they had a supergirl movie and was not a success.