The studio is reportedly trying to convince Christian Bale to return in one last performance as Bruce Wayne, while the new Man of Steel, Henry Cavill, will star as Superman. If Christian Bale declines to return, the studio will seek out a new actor to portray Batman.
It is said that two separate versions are being crafted, one where Batman mentors an up-and-coming Superman, and another where Superman mentors Batman. It isn't known if there are screenwriters attached at this time.
The project is in very early stages of development, and they still plan on moving forward with The Flash and Justice League of America before this untitled endeavor. Warner Bros. also plans on rebooting the Batman franchise after The Dark Knight Rises, which will be the last adventure with star Christian Bale and director Christopher Nolan.