Some years ago I made an addon to manage an online registry of addons. It seemed natural to me (and still does) that addons could be downloaded on the fly inside Blender, rather than either having bundled addons (i.e. downloaded and installed by design, but I don't use most of them) or having no standard way to install addons retrieved from internet.
I did not received any feedback from Blender developers so I didn't push this addon forward, but I just discovered this website so here it is again.
Not sure if it directly works, e.g. GitHub may have changed something in the URL for accessing the registry JSON. Anyway, it was just a proof of concept, hopefully you will like it and adopt this concept into Blender, i.e. redesign the addon window a bit, host the registry on assets.blender.org or something, etc.