I'm also starting to think that there is a story to be told post-TDK. It's starting to come together now that everyones mentioning it.
Doesnt Bruce say to Talia that he could have flooded the reactor anytime in the last 5 years? So he wasnt completely out of the business side of things for the entire 8 years. The first few years he could have been doing his thing, as well as being Batman.
It might be the publics perception, they just havent seen the Batman since that night. But Batman is a damn ninja, maybe he went more low-key without getting noticed with the massive vehicles. Probably no bat-pod, no tumbler.
Then you have the knee brace, which i feel is from that night with Two-Face but it would be easy to add in a story where he doesnt go to the hospital for his leg, and some other rogue makes that knee much worse.
The Dent Act also doesnt come into play right away. And last.. Alfreds line to Bruce about him not being down in the batcave for a while. Well..that's a little weird. So obviously once the cave was ready, Bruce had all of his gear put there and set up the computers. But it sounds like Alfred could be refferring to him being in the cave before, working on the computers in Batman detective mode, and that he hasnt done that in a while. I dont know, maybe there is a story to be told about a year or two after TDK with Riddler or a final mobster.