Core Data threading? Does Linux even attempt something like Core Data? How well is that going?
Swift? I remember when Linux diehards invented Vala. The Swift of Linux, but with none of the adoption.
As for UI code, Linux is finally starting to get a little more stable there. GTK 2 to 3 was a disaster; Qt wasn't fun between major upgrades; if you weren't using a framework, you needed to have fun learning the quirks of Xorg; nobody who builds for Linux gets to lecture Mac about UI stability.
Or, for that matter, app stability in general. Will a specific build of Blender outside of a Flatpak still work on the Linux desktop after 2 release cycles? No? Then don't lecture me about good practices. Don't lecture me about how my website or app was sloppily engineered because it has dependencies.