[jiehong]

I think one of the point of the author is making might also be that a window manager could do just more, like managing windows as tabs as well.

So that any application could have tabs, if the desktop manager would allow you to group windows as such. Same with showing a split view within such a tab as well.

I think I agree with that. I could imaging that the browser containers of tabs would make a ton of sense if I could make a container of windows handled as tabs across different applications at the window manager level.