I had a similar idea about using JSON Schema to validate my API. However, a few issues that I thought of and a few I discovered while researching:
1) I am not aware of a decent JSON Schema editor. It has been on my wishlist/TODO list for a looong time to write one myself which has similar capability to something like Oxygen for XML [1], but I have not had the time. Do you plan to write and update the JSON Schema by hand?
2) I have not researched them in great detail yet, but Swagger [2] and API Doc [3] seem to have already defined something similar to what I had in mind with JSON Schema. Have you looked into those tools yet?
[1] http://www.oxygenxml.com/index.html [2] https://helloreverb.com/developers/swagger [3] http://apidoc.me/doc/gettingStarted