People have been hailing the death of Windows and the beginning of Linux's rise to the top since the early 1990s. (Remember slackware and their "f**k you, figure it out yourself" welcome message?)
Yet.. here we are. Value is pouring R&D money in Linux... for Steam. With Steam being the front end and operating system (more or less). The Steam Box may die and early death due to the RAM prices skyrocketing due to the AI data-center slop rush currently happening right now. We'll see. But the Steam Box (Steam Console?) is going to be more akin to Apple Mac than Linux. Its going to be a fit-for-purpose OS on fit-for-purpose hardware. Most people aren't going to buy a Steam Box to NOT use Steam big picture. That's the whole point. They'd just buy a regular computer instead... and SteamOS is only putting in drivers for the hardware they're selling.
Anyway, long story short. Yes, it would be great to have a mainstream alternative to Windows. But Linux ain't there yet, and probably never will be since the solution to every major problem is "these guys are doing it wrong, I'll make my own fork and do it right!" (insert Bender quote here) - and now we've got thousands of forks.