- What we definitely need, imo, are commentaries indeed. Christopher Nolan, Jonathan Nolan and David Goyer all doing one commentary for each film and maybe Christian Bale doing another just by himself, his views of Batman's villains in each film, and Bruce Wayne's arc of the entire trilogy.
- New transfers would be amazing, although I always thought BB needed one more than TDK.
- Behind the scenes, but only through featurettes, I think, would be a given. I think an ultimate collection should have plenty of featurettes.
What I HOPE for, but I don't know if it'll be a for sure thing:
- Some kind of feature speaking of a retrospective as you mentioned. I don't think it will be necessary, but it would be nice nonetheless.
- Michael Caine and Morgan Freeman commentary for all three films
t:
- A "Gotham Live" featurette. A news snippet speaking on the events after the siege that TDKR didn't have time to delve into.
- Deleted scenes. I doubt Nolan will add them into the final cuts and make extended versions, but it would be nice to see ALL of the deleted scenes from all three films. Joker leaving the penthouse and entering a car to leave comes to mind.
- A retrospective on the evolution of all the characters from the trilogy that were in the comics. Going from when they were created and down the line to how Nolan perceived them.