Sure, API Blueprint supports JSON Schema. If you're happy to put in the effort, nothing stops you from using JSON Schema in the blueprint and all the tooling built on top of it.
sometimes i think it would make just as much if not sense to define these communication protocols with a bnf grammar (for endpoints and response codes) or to use s-expressions (since json is pretty much just sugared lisp) or some other well-worn-but-adaptable format just because there are already parser generators and scheme interpreters written for every language.