I have a feeling it may be someone of actual relevance. Outing a character is hardly anything new. It's always been a b-lister though, unless you count X-Men's Colossus in the Ultimate universe.
I'm hoping it's Wonder Woman, that'd be hawt. I wouldn't be TOOO shocked if it were Bruce, after all he's single, thin and neat.
In other Batman news, they're making a direct to DVD animated movie of "The Dark Knight Returns"
http://www.hollywoodreporter.com/heat-vision/dark-knight-returns-peter-weller-327960