Yeah, they definitely don't need to bother with origins anymore. Hit the ground running with a comic-faithful, older Batman who's been active for years.
The first movie gives a passing reference to the Joker having disappeared.
The second movie doesn't mention him at all and seemingly wraps up nicely, before a dark, unforeseen, Spider-Man 2 style cliffhanger:
Cut to black on the iconic 'smile' image:
Then leave the audience to stew on that
for three years, before the third goes for all-out, Bats vs Joker awesomeness.