Good idea. But come back after you see it. Spoilers to follow.
Here’s what I think is the real road block to TDKR being the “next” movie - they haven’t soaked the franchise enough to want to get to the final episode.
Having said that, if they ever make TDKR, The Joker would be significantly older too, which may enable them to address the late HL problem.
But boy, if they do make it, what a challenge. Start with length. Move on to Harvey Dent needs to be alive. They will be tempted to “write out” the Mutants (as passe?) and, of course, they are right at the center of the saga, especially the leader. Also, the Robin character is terrific and I fear she would be written out.
Finally on bad guys in Batman. The eternal problem is that in the hands of competent writers The Joker and Harvey Dent are the 2 best villains in the series. In fact I bet we all agree that The Joker has become one of the most compelling villains in fiction - period. You get past them and the others, as written to date, pale (no pun intended) in comparison.
Except that a case can be made for The Penguin. Tim Burton came close to a great villain with The Penguin in Batman Returns - but did not quite pull it off. A “deformed” from birth, abandoned by parents character, who is so furious at the world that he spits black bile when he talks, has real possibilities in my view. Most of the time there was nothing goofy or squawky about Danny Devito’s Penguin. The Nolans might be able to perfect what Burton started.
As for Batwoman, Michelle Pfeiffer’s portrayal, as directed by Burton, I thought was terrific (and creepy). So, there’s no reason not to bring the character back - just not as the lead.