Is there a benefit to describing APIs using YAML instead of just, y'know, prose? Seems like basically all you can do is generate HTML docs from YAML. Ok, so let me get this straight: instead of writing docs, I write YAML... --Either way I write 1 thing,--but now I can only create docs from the problem space of the known YAML schema. So it's a lossy abstraction.
Looking around I see you can now do some basic code gen of models in any language, as long as that language is python or matches the regex /java/ . But usually these messaging systems already use some data format with schemas and code gen tools like protobuff or avro! It's not just redundant, it's a collision, because something might not match up right.
Unless there's something else, it seems like something I'd advise to NOT use.