As it stands, Bane's and Talia's motivations don't quite make sense, I think. We're told they want to bring harmony by bringing down the corrupt, and yet they still want to destroy Gotham even after bringing down its corrupt aristocracy. It would have been fixed by something as simple a line as, "See how corrupt Gotham is? They let their plutocrats rule with impunity -- and when I bring down the powerful, the people become just as corrupt as their former oppressors! Gotham must burn." Or some such.
The aristocracy was never their target. Ra's and the League regarded the whole city as the problem, whether through participation or acquiesence (hence, Bane using the freed criminals as labour force, even though they are also among the biggest offenders). The original plan in the first movie involved destroying the entire population. Bane just turns one segment against another as part of his plan for slow destruction. Talia and Bane's actions are entirely in line with what Ra's al Ghul wanted before (amplified by their desire to avenge him).
Replacing Talia with the Joker discards the whole thematic point of the movie, the return to where it all started.