Alright, I have a mismatched setup: a 1080p and a 4K screen. No matter how you twist it, the virtual screen* will have dead zones. Self-management of a single full-screen canvas is easy (browser F11). But then I will want to use the entire physical screen estate with the editor and it'll end up re-implementing large parts of the window manager just to position the windows where they belong, rendering at the correct monitor DPI.
Further, just from the shown animation I can already see the same problems you'd encounter with a lot of screen space and old style window managers: you grow tired _very fast_ of moving and resizing additional windows yourself to fit more on the screen. "Maximize (on current screen)" is the only automation step in this direction and it is decades old. Windows' "snap to edges" is a semi-manual attempt at assisted window management.
* in Win32 terms, a rectangle encompassing the entire region with all visible screens
Further, just from the shown animation I can already see the same problems you'd encounter with a lot of screen space and old style window managers: you grow tired _very fast_ of moving and resizing additional windows yourself to fit more on the screen. "Maximize (on current screen)" is the only automation step in this direction and it is decades old. Windows' "snap to edges" is a semi-manual attempt at assisted window management.
* in Win32 terms, a rectangle encompassing the entire region with all visible screens