It's probably more likely that Microsoft will ship a Swift runtime/compiler system for Swift than Apple admitting anyone cares about anything but iOS. I'd be slightly surprised if MS hasn't already started on it.

The day Apple goes cross plat will be interesting. (Sorta like MS backing down on longstanding issues as reality invades.)

I think it's coming. There was a HN post about MS working on bringing Obj-C to MS without any kind of emulation layer simply by leveraging llvm and the existing MS C++ compiler. It's called Project Islandwood (https://dev.windows.com/en-us/uwp-bridges/project-islandwood) and in a video presentation about it there was also mention of work on Swift (although Swift support wasn't official). MS is really moving in some interesting directions these days and I'm all for it.

With LLVM as a back end this should be trival.