While I bet going the Batman Beyond route is more likey to happen, I'd LOVE LOVE LOVE to see a feature film play on a turn of the century Batman tale, ala the old Gotham by Gaslight story with Jack the Ripper or the Batman meets Harry Houdini comic.
Those are two of my favorite Batman storylines and done properly, would be awesome to watch.. Done properly, some steampunk elements could be woven in to add atmosphere (so to speak), but most movies seem to overdo steampunk weapons and technology (see Van Helsing)...
That could be fun. While I don't know about a live-action feature it would be fun to see the the animated films take a crack at some Elsworlds like stories.
But not likely to happen.