As far as I can tell, currently official Home Assistant integrations are baked into Home Assistant itself. This is not exactly an ideal situation from a development point of view, nor from a user’s point of view. It means that integration updates are tied to Home Assistant updates, which leads to lower reaction time to real time issues. I propose instead using a package management like system instead similar to pip, npm, or nuget.
Treating integrations as packages that can be installed and updated on an ad-hoc bases increases flexibility of the system. Part of that flexibility would also be the ability to easily add third-party feeds. If a standardized method is created, you could just use a URL to add additional community driven feeds. Which would greatly simplify the process of adding and using HACS.