A very cool visual cameo in the movie I am Legend starring Will Smith (click to enlarge):
As AICN notes it probably isn’t a viral tease for something already in production, but given that both franchises are successfully rebooted and are doing well, there’s certainly a possibility. I wouldn’t accept anyone else playing Batman besides Christian Bale, as he owins that role. As far as Supes, Brandon Routh did a good job of channeling Christopher Reeve (almost too good) but I’m not particularly invested in that representation. The interpretation of Supes as Kent being the disguise never sat well with me. I prefer the route taken on TV (Lois and Clark and Smallville) where Clark Kent is who he is, Superman is what he does. We haven’t had a Superman of that sort on the big screen before and that would I think be the better complement to Batman in a combo film.