Windows NT had overlapped IO decades before Linux. The Microsoft kernel team were alright.
If we're just strictly talking about low level things, another good one would be synchronization primitives, which I guess we now have some of in Linux verbatim at this point, if only for the sake of emulation. (And of course futex2.)
Think of ctrl-alt-f7, f8 etc. This still works today, you can run X servers as different users on different VT numbers and switch between them. All that's missing is better UI.
I was talking about this:
https://news.ycombinator.com/item?id=49093002
And it winds up being mostly a thing you have to implement in the compositor, but none of them do so far to my knowledge.
And of course the same issue applies if you wanted multiple physical seats juggling sessions between them.
It's kind of the opposite, systemd-logind provides better seat management than without. I attempted to implement the same concept using libseat and seatd unsuccessfully though I do not remember exactly what I got caught on. (not in kwin but a toy compositor; I have been at this problem for a little while now.)
That said, most desktop systems have only implemented systemd-logind in a limited way so far that basically just does what the VT system + display manager was already doing, that's what would need to be worked on in order to make this a reality. I was able to accomplish a prototype with only patches to Kwin, kfreerdp and plasma-login-manager, no need to patch systemd-logind or anything like that.
> Who even uses systemd?
Well for one thing, almost all of the major distributions; Ubuntu, Debian, Fedora/RHEL, Arch Linux, NixOS, openSuSE? and of course SteamOS now.
The only major non-systemd Linux distributions I can think of are Alpine Linux and Gentoo. And Android if you wanted to count that, but I think it is special enough to be considered its own OS that just is Linux-based.
I certainly wouldn't DIY this; nothing would support my DIY version, which would defeat the purpose.
Linux strengths: file system, open source ecosystem, ssh, lockless algorithm support
The main features that were better in Windows NT than in the UNIX-derived operating systems were inherited from the DEC VAX/VMS operating system (1978) (e.g. WaitForMultipleObjects) and a part of them had been inherited from the even earlier operating system DEC RSX-11M (1974-11) (Dave Cutler also had a major role in those operating systems, so there is nothing surprising about this; Microsoft had to pay a big compensation to DEC, on the order of $ 100M, for the features that were obviously taken from the DEC operating systems).
UNIX was very simplified in comparison with the operating systems that were used on bigger computers, and for some things its derivatives never caught up with those older systems, except after 2000. Only "futex" (2002) and "io_uring" (2019) have advanced the state of the art clearly beyond what already existed for AIO on the IBM mainframes around 1964/1966.
It's an evergreen interesting fact that Dave Cutler took perhaps a bit too much inspiration from prior VMS work to NT, but I also think there's no need to put an asterisk on it anymore than there is UNIX or anything else; it does ultimately stand on its own. Like great artists, great software architects steal.