I don't see why The Joker needs
to return. I think it would be fun if he did, but only if Heath Ledger were still alive. I think seeing someone else as The Joker in a future Nolan-directed Batman
film, besides being completely inplausible, just wouldn't work. Rachel Dawes was recast because the actress playing the part no longer had any interest in reprising the role. This is different. Heath Ledger isn't not interested, he's no longer with us. I think having another actor portray the role right after
his performance would be seen as disrespecting his memory. I might not particularly agree with it, but I believe that would be the public perception.
With that said, there are a plethora of villains and stories out there. Considering that Nolan probably has one more Batman
movie in him (if that), I don't want to see it wasted on characters we've seen before. Revisiting The Scarecrow was fun, but it was also only for one scene. We didn't have to sit through another movie with him, and I say this because films are a different medium... It's one thing in the comics to have villains reappear and take center stage for an issue or two, but these movies are made so sparingly and few & far between that I want to see something new and fresh. Having characters like The Scarecrow reappear, like I said, is fun, but not for the entire film. If Heath were alive, I'd love to see him making a Hannibal Lecter-esque return for a scene or so. But he's not, so out of respect for his memory and his performance, let's move on, shall we?
One thing I do hope is that he is at least acknowledged
in the next fillm. I hated that Stryker or really anything in X2
was really left out or not mentioned in X-Men: The Last Stand.
Since honestly, if it wasn't for Stryker, there would be no X-Men: The Last Stand.
It's a bad analogy, but The Joker made a huge impact on the events of The Dark Knight
and the events that will proceed, so I think a passing mention of him is a bit necessary. However, in retrospect, Ra's al Ghul's "contributions" to Batman Begins
opened up the floodgates for what happened with the criminal and mob element in The Dark Knight,
and he wasn't mentioned, as Bad Bishop
accurately pointed out, so perhaps The Joker doesn't even need a passing mention.
I'd say...let Nolan figure it out. That's what he's good at, anyway.