1. The Avengers movie must be a success. I think the reason for this is obvious, a large ensemble cast CBM; if it fails DC will be scared off any ensemble cast movies.
2. The new Superman movie MUST be set in a world where there are other hero’s; this can be accomplished by simply referencing Gotham City.
Batman is the most successful CBM franchise to date with 6 movies and a 7th in pre-production. Granted not all of them are worthy of being in included, but they were, like it or not, Batman movies. WB may be many things but they are not stupid when it comes to making money. After the next Batman movie, “The Dark knight Rises” has come and gone, (and Nolan does not do another one) there WILL be a Batman reboot. There is just too much money to be made not to. At that point Batman can be set in any world they want, even a world with other hero’s in it.
Superman is the lynch pin. If the new Superman movie is a success (and we all pray that it is) there are guaranteed to be sequels. If Superman is in a world by himself, then we will not see a JLA movie in our lifetime. We would have to wait for the sequels to run its course, and then wait for another re-boot. Current patterns say there will be a trilogy and with at least 2 yrs. between movies and another 3 for a re-boot we are looking at 9 or 10 yrs before Superman meet Batman, but remember in those 9-10 yrs the re-boot of Batman will have also run its course so we would have to have another Batman re-boot. You can start to see where I am going with this. Like I said, “Not in our lifetime”.
The Flash movie is on again off again; who the hell really knows about Aquaman, and Wonder Woman is now going to TV .The only other JLA member with a movie at this point is Green Lantern. Now I will be honest and say I do not remember if GL is set in a world with no other hero’s or not; but given the nature of GL and its cast of alien characters, it would not be a stretch of the imagination to say that there is. The Flash, Aquaman and anybody else could be introduced in the movie (kind of like what they will be doing with Hawkeye, in the Avengers) Martian Manhunter and Wonder Woman are more difficult since their origins are not so obvious.
Including Batman in Superman’s world does not have to be a complicated thing. In fact it can be done with 2 words “Gotham City” that’s it 2 words. You do not have to make any references to Batman. But by mentioning Gotham it implies that since there is a Gotham City, there is a Batman. This leaves a “plot door” open for there to be Batman without ever mentioning him, and what is more, it doesn’t even have to be used. When they re-boot Batman and they will, doing the same kind of thing, just a mention of Metropolis will imply the presence of Superman. It just makes sense to me, why tie your hands when 1 or 2 words can open up a world of possibilities, and a JLA movie.