I am willing to accept that proposition in principle (though it basically rules out certain classes of apps from being nice on Android IMO).

For sake of argument, let's say that these design systems serve as proving grounds for new platforms. In that case I think there's some interesting discussion to be had!

The upteen complaints about things like Gnome 3 or Android's material design. Hell, lots of complaints about iOS 7 at that transition. If there are strong alternative design systems out there, those can be pushed forward