When did the ability to clone a repo outside of GitHub become a niche use case? It's not something you need to explicitly support, in fact you have to actively go out of your way to make sure only GitHub works.
Inko's package manager supports non-GitHub repositories just fine. What the original comment likely is referring to is the website only including GitHub based packages. This is simply because the script that populates that list hasn't been extended to support more than GitHub, because there hasn't been a need for it so far.