I'm always interested when it comes up, especially when I see info on its progress for usability on non-Apple systems, but the last time I remember seeing info on that (multiple months ago, admittedly) was that it was coming along, but there wasn't quite parity with the Apple ecosystem and some (core?) libraries were different/not as good?

The impression I got (from comments of here trying to use it) was sort of an early Mono .NET type of situation (maybe not that forked, but still). It's hard to put any effort behind learning a language when it feels like you would be a second class user. I spent way too much time and effort being the guy trying out the experimental Linux support for projects inthe late 90's early 2000's, and I have less time now, so my explorations need to be a bit more directed.

It came down to Swift or Rust for learning a new language a while back for me, and I picked Rust for the reasons above. I've yet to do anything with it (and I'll have to brush up on it yet again when I do), but at least I don't feel like I'm getting second class support from the language.

I wouldn't mind being mistaken or having this already been addressed and Swift's port to other systems is at parity with Apple's. That would be nice. I wouldn't mind spending some extra time on it then, it does look to be an interesting language.