Plugin Manager 2
As of release 2.1.8 there is a plugin manager. It's available as feature extension. Once acticated (after a restart) it brings up a new 📦 Add tab in the configuration window.
You can scan for available/new plugins there. And have them downloaded right away. New plugins are just downloaded, not implictly enabled. Reopen the config dialog to see them in the regular lists.
Configuration
Alternative download repositories may be configured. (Little practical value at the moment and foreseeable future.)
And you can let the plugin manager handle regular plugins as well. After reconfiguring existing channel plugins, they get automatically run, or disabled in the user interface (without any restart). Which won't work for most feature/core plugins.