While I prefer tiling windows manager, GNOME’s approach is sensible. Restrain your features to a restricted default and allow users to extend it if they want to. The code is open and well organized as far as I can see. So it’s very easy to see where to extend from.
I can do that on GNOME and macOS. And yes, with 21:9 it is very nice. With a vertical monitor or a 3:2 (Surface), not so much.