I don't really care that much about which genre, but I would love to see Nolan do something different. Every movie of his since TDK has gotten bigger and louder, and it would be interesting with a slightly smaller movie (at least in scale) with someone else rather than Hans Zimmer doing the music, or just a very different kind of soundtrack. Don't get me wrong, the soundtrack to Interstellar was amazing, but it's like Nolan has gotten into a certain "phase" right now, it would be nice to see him do something completely different.
No massive dream worlds, no cities under siege with atom bombs, no saving the earth missions to space. Just something smaller in scale.