That is not a theme, but I think there was obvious symmetry to Ra's plan on purpose from Bane and talia.
It's the same plan, just executed slightly differently (the siege).
When he talked about bringing a better class of criminal, he's talking about those who do it for reasons other than money or power.
I know. Rather obvious considering he just burned a huge pile of money and then said to the Chechen; "All you care about is money. This town deserves a better class of criminal, and I'm going to give it to them".
Bringing in Bane and Talia delivers on that promise.
How? They just wanted to destroy Gotham. The Joker never ever wanted that.
But it's also a line that he says in referring mainly just to himself - it's not necessarily that he wanted many more criminals like him, he just thought of himself as being more than a superficial criminal.
Obviously he was referring to himself, but it seemed obvious he was also talking about inspiring other criminals for the same. TDK was all about inspiration and reactions. Batman inspired copycats. Joker was the reaction to Batman. Dent inspired Gotham's hope more than Batman could etc. When Joker talks about better classes of criminal, it seemed obvious he was talking about more than just himself.
And yes, I agree Joker did much more than that - he made Bruce and Gordon both compromise their values, thus winning. His job was done. He had made the three people who were Gothams' hope turn against what they believed in.
Indeed. But without Gotham's people knowing that, he was denied his ultimate victory. The way they left him alive, captured, knowing what Dent had become, and saying he and Batman were destined for a life long battle, it left the strong impression/message that Joker was not done.
Heath's death put an end to it.
Look I'm sure the Nolans could have found a way to do it well. I just don't really think it's that obvious that they would have. I'm sure the studio would have wanted it, and they would have tried it. But at the end of the day, I haven't heard a single example or reason the third film would be better for it (besides the obvious that Joker is awesome).
Much like I haven't heard a single reason why retreading the LOS was a good idea other than the "full circle" excuse which is not needed to make a trilogy feel connected and complete.
The Joker had unfinished work which we saw happen in TDK. It got covered up. Begins didn't leave anything like that dangling with the LOS. As far as it was concerned the only dangling threads left there was Crane on the loose. But it also set up future plot threads like a new D.A. being needed since Finch was murdered, the escalation Gordon mentioned, a new mob boss to fill in for Falcone, and the Joker card at the end. Like any good sequel, TDK dealt with all of that. It felt like a natural organic progression of the story in Batman Begins.
Bane and Talia were not hinted at in any way in Begins. They were created in TDKR.