The problem is Spidermonkey for windows, as their build is pretty opaque, and they started calling some Windows APIs breaking compatibility. You get a nasty error if you try to run something there about a missing Kernel32 function

For macOS, you can actually build for > 10.12 BUT the build will only be compatible with this. See https://code.wildfiregames.com/D2827 for more info about why the SDL2 broke stuff.

Thanks for the detailed response!

I guess that'd be pretty challenging now with all the new requirements noted in the "Under the hood" section of the release notes.