One is a complete character and history change ... the other fixes the biggest issue with Bane, that his "weakness" is out in plain sight. The Joker's never had a real "origin" story - and by that rational, TDK played it perfectly. Nolan isn't going to just all of a sudden introduce Nightwing out of the blue. There is nothing in his cinematic history to even suggest such a thought.
Wasn't the Joker just mentioned out of the blue? Yea, everyone saw that coming and it was expected, but still, the last 2 minutes BB talked about the Joker with no other mention of him before that. It's all speculation so I'll stop, neither you or I are right or wrong on this.