I've been saying for a while now that the open source world would have benefited if more effort than what went into GNUStep had been focused on copying Cocoa to the point that it rather than GTK or Qt had been the toolkit of choice for the Linux Desktop. Especially when there was a major infusion of interest circa 2010 of folks adopting the MacBook Pro as the developer machine of choice.
I think it's still doable. And I mean down to looks, too, and not just API feel. Aqua from the same time period (Snow Leopard through Mountain Lion era) is the closest thing I can think of to timeless visual design.
It's true that if everyone just made Cocoa apps that looked like they were created with Mac OS in mind it would look out of place on Windows and elsewhere, but (a) it would still look rather good, and (b) it would not look any more out of place than anything else, including Electron and even lots of "native" apps, due to the proliferation of toolkits described in the article not to mention the Gnome identity crisis that has only just recently begun to get reigned in—mostly by following Mac OS cues and being more consistent than before. It's just a shame that it stops at the surface level and doesn't carry over into the actual APIs. Plus those cues are from the post-flattening of UI.
