Swift has this weird sort of ecosystem where Apple builds much of the platform in a very secret (most of the roadmap isn't shared), closed-source variant for its own OS. Then it has this open source version, with a very public compiler (roadmap IS shared) that allows cross platform toolchains like this one to exist. I call it out as weird because take SwiftUI for example, the main excuse Apple engineers gave for why…
SwiftUI is just a closed source framework. What's so confusing here? We don't expect Microsoft to develop its proprietary APIs out in the open despite it having a large presence in the open source world, why would we of Apple?
> On the other, I'm not entirely sure what the point of this effort is for?!
To develop using Swift on Windows. It's not terribly difficult to imagine that people might enjoy using their preferred language on other platforms — you mentioned Rust, after all, and that's on practically everything.
I think the confusion you have is not understanding the boundaries between Swift (the open language) and SwiftUI (the closed framework) — which, honestly, given the names, I can completely understand.