My only problems with The Dark Knight Rises
had to with Bruce Wayne and Bruce Wayne alone. Since he's the main character, it guts the movie in my eyes. It also pisses away what was built up in the last two movies.
John Blake is a different matter. If they wanted to do a spin-off movie with him as Nightwing, I'd look forward to that. I doubt he'll be Batman.
I'm guessing the next Batman movie will be spun-off from a Justice League
film, to ease the transition for the audience into a reboot. Otherwise, jumping in cold from TDKR to whatever the next version of Batman is will feel too much like whiplash.