I had some contribution that allows end-users managing service definitions without restarting the Knox Gateway. See
KNOX-2053 and KNOX-2056 for further details.
I've been just about creating a new JIRA to document those new API endpoints in the Knox user guide but it has come to my mind that we can do it much better by using Swagger.
Given the fact, the Admin/Metadata API does not consist of hundreds of existing endpoints it should not be 'that' huge work. I personally believe the project would gain a lot by using this very useful tool. This way the Admin/Metadata API documentation would be generated out-of-the-box, no more documentation JIRAs required. Moreover, the generated documentation would be in sync with the actual implementation.
You can check this out here: https://swagger.io/tools/swagger-ui/ (there is a live demo too; it's worth looking at).