Re: They are going ahead with a Justice League movie
They'll do something because as it stands 'The Man of Steel' is the only DC movie they'll have to lead into this. Every Marvel movie was doing this from the beginning. I think they've got to do something similar to get attention to the film.
Avengers had scenes added at the last minute for the after credits so I don't see why they can't something quickly like that with MOS.
"It's not that you can see the strings, it's that 40 years later you're still looking at them." - Steven Moffat
"This movie was big. Imagine how big it could have been with me in it?" William Shatner