Nolan's universe was too grounded to bring in Bale or anyone from that universe in general. They'll have to bring in a new Batman or reboot it which is why I don't think this is such a good idea so soon. TDKR just came out in 2012 and by the time this movie comes out, it would be three years since Rises. For comparison, some people thought the Spiderman reboot was too soon and that came six years after the Raimi trilogy. That's why I'm cautiously optimistic about if this movie will be handled well. Marvel built up to the Avengers nearly perfectly. I really wish DC would not rush this opportunity because the Justice League movie could be bigger than the Avengers if they took their time to build up to it. As a side note, the next Avengers will be called Avengers: Age of Ultron. Ultron was like the last villain that crossed my mind to be in the next Avengers.