There's so many rumors popping up,
This article has a couple of them
For those who don't want to bother with the link, the Wachowiskis are supposedly involved (and I really don't think that sounds too good. They haven't really had success with anything after the first Matrix, arguably the second... and I heard, rather read, what their plans for a Plastic Man movie was going to be like). And secondly, they plan to use this film to relaunch the inevitable Batman reboot (who is too important to DC's film empire to just let alone after The Dark Knight Rises).
Now, again, this problem lies within the success of the next Superman movie, not to mention the problem with the Green Lantern film, where they still don't know if they want to reboot it (making us suffer the long and winding origin again) or make a sequel (which will HAVE to be better than the first one and completely salvage the franchise). If the new Superman fails, this movie has no legs to stand on. It does itself a disservice to try and ape The Avengers, which at least ran on to footing of 2 successful Iron Man films, and (while they were made to coincide with Avengers) Thor and Captain America doing very well and being solid films.
Of course, I thought of a solution for the Green Lantern (that won't happen, but logically should) that could salvage this film. Instead of doing just a direct sequel, have Ryan Reynolds back as Hal Jordan, but
also have either Jon Stewart or Guy Gardener get inducted halfway through the film as Green Lanterns... only to have either Jon or Guy as the Green Lantern in the Justice League (leaning more towards Jon to get
some ethnicity in the film).
Or, again, just start with the movie first as a launching pad for reboots and get Paul Dini to write it. Having Paul write the script is basically Warner Bros getting a license to print cash.