I think it would be great to have a marketplace on your site where testrail users can post things we have written on top of the TestRail API.
For example, I would love to post
- plugins for Jenkins, TeamCity, Bamboo which can upload results directly from CI to TestRail
- report templates for next release of TestRail
- sample code in JAVA/C#/Python/etc
Most people will probably just post for free but I can see many who would like to make some $$$. Similar to how you can do this for Bamboo/Teamcity, etc