alt Hacker NewsI 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.
Windows (IE) tried to give WM visibility into tabs long ago, but this quickly revealed a problem: if tabs are now also separate windows, they enter the Alt+Tab ring, and suddenly you're Alt+Tabbing between 5 applications and dozens of open tabs. N=1, as a tab hoader, I absolutely hated it (it also made Alt+Tab itself very slow to show and cycle).
The general problem is that having WM handle in-app tabs means the WM has to support every single hare-brained idea about meaning and role of tabs that app developers invent, which is infeasible. Even with browsers - until recently, you had like just two types of tabs: regular tabs, and porn-mode (er, "private browsing") tabs. Then came "account containers" or whatever it was in Firefox. Then came tab groups, reading groups, and tons of other nonsense.
OTOH, I can dream of an ideal world where the OS manages all tabs for all apps via combination of Sidebery (better "tree style tabs") and a tiling WM.