The idea of Robin wouldn't work in the Nolan films, but you do loose the idea of Bruce creating a sort of family around him.
In the comics he ends up with Gordon, Alfred, Batgirl, Oracle, Robin, Nightwing, and on ocassion Huntress, Question, Azreal, and even Catwoman.
That is sort of cool, but the way to introduce that would be bringing in Robin and that wouldn't work.
Reasons why Batman might even consider bringing in Robin are there maybe, I could see Batman thinking that some day he would need a replacement. An apprentice perhaps, and maybe even a partner to help him clean up the city and take some of the pressure off.
And I could see Robin being brought in to sort of help Bruce get back out of the Batcave. Sort of like being a Big Brother to Dick Grayson, maybe Alfred signed Bruce up.
But
Bruce would never allow another person into his war on crime. For one its too dangerous and he would feel too responcible, and then what if that person got hurt. Another reason is he would be too much of a control freak to allow another person work on mission.
But I still like the idea of a Bat-Family.