My pitch for these edits is this: all live-action Batman films (Adam West aside) as one, consistent series. It would be all about bridging the vastly different styles of each director into one coherent vision. So what changes?
Gotham: The city of Gotham should look exactly like it did in the Burton films. In fact, the whole aesthetic of each film should match theirs as much as possible. This would mainly consist of swapping out establishing shots.
Music: Once again, the Burton films are the standard. Danny Elfman throughout, or at least his style. His main theme especially should be prominently featured in each film, most notably over the opening credits. This is probably the easiest change to make, as it’s just swapping music.
Continuity: Look, I’m not gonna deepfake everyone to have the same face throughout (although if someone wants to give that a shot, I’ll gladly have a look). We’ve all seen James Bond change actors, we can look past it. What’s harder to look past is the vastly different designs of the villains, namely Joker, Two-Face, and Catwoman. I’m not sure how feasible it is to change their designs to be more consistent but it’d be worth a shot. I’d say our best option for the Joker is to bleach the Ledger Joker (black around the eyes included). As for Two-Face, just make the Jones version’s scar grey instead of that garish pink. As for Williams’s version, his role is so minor you can just cut it. Obviously, neither character would die in their first film, with Joker successfully boarding the helicopter in '89 and Two-Face surviving his fall and being taken to Arkham. Catwoman already survives Returns and her redesign would simply be a new (inferior) costume.
As an aside, I’m still watching the films so I have yet to see TDKR and the Schumacher films. There might be something I’m missing because of it.