That ending was perfect in that it concluded Bruces story as Batman and his life in Gotham. The whole point of the end, and the movie in general was when Alfred (in the batcave) tells Bruce that he never wanted him to come back to Gotham. He would take a vacation every year back when Bruce was in his 20s and away, and Alfred would hope to see him living his life in peace. And guess what? It happens at the end.
Bruce returning to Gotham either to take back the mantle as Batman or to just get involved in things would ruin the point of TDKR. It would spit all over it.
But it really made me want to see the story continue inside Gotham. And with Blake as the new protector. Whether that be as a new version of Batman or a spin-off as Nightwing? I don't know. But i wouldnt mind a new director coming along for a sequel or two. It's not a reboot, it's a sequel to The Dark Knight Rises but it would be without Wayne so it can still be looked at as a reinvention of the franchise.
These are my ideas..
Gotham now needs to be rebuilt, the US government will get involved now and help rebuild a large portion of the city. This is a easy excuse for the next movie to have a different tone or look for the city. Maybe a much more futuristic look. A new director, new DP, new writers, ALL coming together for this new tone and it'll make sense because it also is a result of where the story is going. Prisoners (like in Begins) will need to be caught and locked back up. This is why Blake (Robin) will be needed.
Gary Oldman and Michael Caine have both said they wouldn't mind doing more movies (i got the impression even if nolan wasnt involved) hell even Bale said he would come back if Nolan had a story. Nolan should leave and he will, therefore at least Bale wont come back. The only way i would enjoy a Bale/Wayne cameo is if Blake travels outside of Gotham to get some training from Bruce. But i would have no problem with Oldman's Gordon coming back for a sequel, reinstated for a little longer. Alfred and Fox can have cameos or if they dont want to return or god forbid their health gets in the way...there's always a way to mention that they have passed away. With Alfred possibly leaving Wayne Manor to Blake because of the whole orphanage thing.
Now, villains? Riddler, Penguin, Mr Freeze? Black Mask or a reinvention of Hush? New characters? Some of them could work. Personally id like to see Riddler, Penguin or Black Mask in this world.
I don't think i would want another trilogy. Nolan seems to be the only one that could pull this off, and even if he tried once more (with another superhero or Bond) i dont think he could do it again. It was like catching lightning in a bottle. A new trilogy would seem like a copy-cat. I think 2 movies could be enough. The first set a few years after the events of TDKR. And a second with an aged Blake. In his 40s, drawing a parallel to Bruce in Rises but not as beat up. Blake training a young Terry McGinnis (or a Terry esque character).
With people like Aronofsky or Refn around, there's a good selection of directors out there who can study the story of Nolans trilogy and see where it takes off from there, while adding a new tone and characters to seperate it and make Gotham evolve. A Batman without Bruce Wayne, in a live-action film is a challenge. A lot of people hate it. Well, you can always call Blake Nightwing if you dont want him to be Batman. Or if you do, it's a chance for them to do something different with Batman. Something that hasn't been done before on the big screen.
The least thing i want is for the next set of movies to bite Burtons style or Shumachers or Nolans trilogy, a realistic setting with a new Bruce/Alfred/Gordon/Joker etc. I want WB and other filmmakers to keep moving forward, and this could be the way. Instead of just rebooting with a young Bruce only to throw him into Justice League and having a fantastical approach. We had that with Burton, we kind of have this in video games with Arkham City. This is a big success this trilogy, people will want more, but us fans dont want the trilogy messed with or Nolan to return or Bale.
Fine! it's an end to that story but there was a cliffhanger there for Gotham and Blake. Somewhere, there is a story to tell with Blake as the new guardian. Whether you tell it on paper only, or on film, it can be told.