Weirdly, the fact that the Windows and MacOS versions will be paid makes me more optimistic.

Customizing at least the Windows window manager isn't for the faint of heart and its architecture doesn't have a lot in common with Linux so such an effort is very far from a straightforward port, and as a result most Linux desktop software and especially stuff that deeply integrates with the desktop environment is basically never ported or the port is incomplete, buggy, short lived, etc.

KDE4 was supposed to fully support Windows and 15+ years later I'm fairly sure that dream is dead.

Custom Windows shells go all the way back to Windows 9x. All you need to do is hide the task bar (or kill explorer.exe) and run your own replacement. Even Microsoft released a downloadable window manager of sorts with PowerZones and they added a registry key at some point so people could stop breaking their updates by replacing explorer.exe and just specify a replacement executable instead.

Custom shells might break some shitty old programs relying on Explorer running as a shell, but the Windows 11 taskbar probably killed those off already.

There are API differences between Linux and Windows of course, but nothing that Linux has that Windows doesn't. As this is based on Qt, a lot of API compatibility will probably already have been taken care of. It just requires someone to go through the effort of writing and maintaining their OS ports.

Both macOS and Windows have alternative window managers available, although macOS does need to be mutilated somewhat heavily to make it happen.

Linux isn't the only F/OSS user-friendly OS; in terms of desktop customization, FreeBSD, NetBSD, OpenBSD, and illumos distros are basically all equally good.