Something to consider is how Sketch.app deals with a extension/plugins ecosystem:
Plugins Directory - this is the official directory for all the extension
https://www.sketchapp.com/extensions/plugins/
They have a github repo with json files as the source of truth for the extension directory, plugin creators are required to submit a pull request to this repo to get their extension included.
https://github.com/sketchplugins/plugin-directory
There is a command line utiltity to help create and publish sketch plugins (to the official repo):
https://github.com/skpm/skpm
Sketch maintains the list (plugin-directory), they don't host the plugin/extension files, those are generally in Git repos. They also have a good interface for turning them on, off, updating them, etc.
This approach has created a vibrant plugin ecosystem and users can easily find, install and keep their plugins up-to-date.
