I tried using a custom "window manager" for Windows a while ago (back in the Vista days IIRC) and it didn't really work well. The main problem was that, as far as I could tell, the window manager couldn't really preempt the windows and force them to show up in a certain way. Instead it basically asked them "pretty please, could you show up at this location with these dimensions?". As a result frozen apps (such as gra…
Yeah, even Windows 10 Tablet Mode is pretty poorly supported in windows apps, and that's just "fullscreen all the things" - it tends to fall over on dialog boxes and the like. Not surprised that more sophisticated alternate window-layout systems would also fail badly.
It's extremely difficult to make any significant change to the paradigm of how Win32 apps are managed and presented and have it work consistently for arbitrary apps - for example they recently tried to add a feature to Windows that allowed arbitrary native apps to be switched and managed via a tab strip like web apps. Worked fine for UWP apps, but when they tried to extend it to arbitrary Win32 they got mired in edge cases and eventually dropped the feature.