Well, of course, most of all I would like to achieve full-fledged support for Xcode Tools (including building iOS applications) and the macOS version of Homebrew. But, of course, there is still a lot of work ahead to get to this point. Thank you!
And it’s an endlessly moving target, look at how many apps break every major release (and use it to justify regular, expensive paid upgrades)
I would look at osxcross[0] if you haven't looked into it already. It can at least do the "build stuff targeting macos" part (well, relatively speaking). Swift support kinda breaks down, unfortunately, and actually getting it set up is a bit of a hassle. but it does work.
[0]: https://github.com/tpoechtrager/osxcross