4. A Shorter Time Jump
Taking inspiration from The Dark Knight Returns, Christopher Nolan jumps forward in time by around eight years for The Dark Knight Rises, showing us a Bruce Wayne who has long been out of the Batman game, before being forced back into the cape and cowl by Bane.
It's an interesting way to give us a different version of the character and examine Wayne's psyche, but it's not something that would work as a more overt continuation of The Dark Knight.
The older iteration of the character plays well against Bane's plan and within the Knightfall elements too, but if you're bringing back the Joker then it needs to be closer to the timeline of the middle chapter, to better keep that story moving and show us how their first meeting has changed the pair.