I was listening to the Modern Myth Media podcast and they had a question about what they thought would happen in a fantasy continuation of The Dark Knight Rises. I had a few initial thoughts that I wanted to share.
I think John Blake (Robin) becomes Batman. He wears the same suit Bruce wears and pledges to clean up Gotham as it recovers from the events of the last two films. He works in Wayne Manor helping out the orphans. That gives him the ability to stay close to the Batcave.
From that starting point, I think there are two things Robin has to confront; cleaning up the city after Bane's destruction of it and maintaining order after the Dent Act is repealed. As part of repealing the Dent Act, all prisoners who were put in prison under the Dent Act are cleared of the crimes they were accused of committing. And the ability to prevent parole is done away with. So it's going to be more difficult to keep criminals in prison.
Those prisoners have already escaped during Bane's takeover. But the police won't be able to do anything to them unless they are suspected of breaking the law again. What Bruce did in TDKR rallies the people of Gotham and they no longer tolerate crime like they did before. But those prisoners are so angry that they begin to try and reestablish organized crime.
But the real threat has yet to be revealed. The Joker has been sitting in a padded cell in Arkham Asylum since the end of TDK. And for the sake of this story, he was put there under the Dent Act. Since the Dent Act has been invalidated in the wake of the truth about Dent coming out, the Joker is released from Arkham. You can probably draw heavily from the comic book "The Dark Knight Returns" in depicting the Joker's release. Miller's comic does a good job of releasing the Joker after many years in Arkham.
I'm not quite sure how you would get the Joker back in the game of becoming the villain since he knows what Batman did in TDKR and since there is no longer a Batman to contend with. So something needs to happen to bring Batman back into the fold, something bigger than just overseeing the released prisoners and normal crime. This could be where you introduce Oswald Cobblepot (aka, the Penguin) as the newest mob boss.
Not only would the Penguin serve as a villain for Batman, he could also be a foil for the Joker. Penguin could be aware of how the Joker played the mob in TDK and thus refuse to work with him in fighting Batman. You could even have him actively fighting against the Joker since he sees him as too much of a threat.
As they say on the Modern Myth Media podcast, at some point the Joker has to figure out that this Batman is not the same person he was fighting in TDK. You can probably have some fun with that. That's all I've got for now.