Having now seen TDKR, I'm convinced more than ever that Nolan's ultimate goal is to do a film-adapt of The Dark Knight Returns
The ending of the film really sets it up perfectly, and several of the scenes shown in the con MoS trailer suggest they want to go that route with Clark.
Plus, for several reasons, Ollie is really big right now and he would be the next-best DC hero to pigeonhole into the Nolanverse. (This of course assuming MoS would be a part of it despite what Nolan has said.)
Throw in Selina's subplot that wasn't fully
resolved and liberally apply it to a certain predicament she found herself in Returns, and suddenly you have your fourth (or fifth
) JLA member.
So "two birds" sort of speak.