it probably wouldn't work to well since the main reason Batman was gone for 8 years was there wasn't any major criminal activity as in no mob and no supervillains.
No, the main reason Batman was gone for 8 years was because he felt he wasn't the right solution for Gotham anymore. Batman was what Gotham needed to pull itself out of the mire and begin its path to recovery, but once the people began to take responsibility for restoring their city to health, and once they had Harvey Dent as a better symbol and inspiration than Batman, then Bruce felt it was time to step aside. That was the whole point of TDK. See, the difference between Nolan's Batman and other versions is that this Bruce saw Batman as a temporary solution at best -- not something Gotham would always need to protect it, but as something Gotham needed to grow beyond. It wasn't until the events of TDKR that he came to realize there was still a need for Batman to exist.
The opening of TDKR makes it clear that Gotham was not without crime in those 8 years -- rather, it still had active organized crime, but the Dent Act gave the police and the courts enough clout to hold it in check. There were still people committing crimes and getting put in prison over those 8 years, which is why the prisons were so full when Bane liberated them. But Batman, by building up Harvey as the hero and himself as the villain, had transferred the responsibility for Gotham's protection from an animal-themed vigilante to the police and judicial system where it belonged.
So yeah, this would basically be a cop show. But it would be a cop show with a potentially interesting premise, about a once deeply corrupt city that's now being aggressively cleaned up, but whose cleanup process is built around reverence for a man who actually became a monster. There's a story there. Maybe not a story that has much to do with Batman, but then, Agents of S.H.I.E.L.D.
doesn't look like it'll have that much to do with Iron Man or Captain America either.
I imagine the Dent Act itself could provoke a backlash from criminals, just as Batman's emergence provoked a backlash. The reaction to Batman was the Joker, the emergence of the supercriminal. Perhaps the reaction to the Dent Act could be the criminals developing a more sophisticated and unified organization of their own to counter it, or operating more subtly to try to stay under its radar, as opposed to the more brazen activities they were free to commit before. I could see a major role for, say, a crime boss called Edward Nygma, sometimes nicknamed Riddler for his devious deceptions and master schemes.