probably not a huge deal, but bigger implications

> Drop support for /etc/passwd and /etc/shadow

You say that as if it's a bad thing.

In the real world, requiring all processes performing authentication to (1) run as root and (2) work with plaintext credentials is both (i) a major security weakness (that has been exploited countless times) and (ii) severely limits the sorts of authentication mechanisms one can use.

> We're progressively but surely going away from the KISS principle that has made UNIX-based systems last 5 decades, and slowly turning them into a single megalith that nobody understands and that newcomers will denounce as the pest to combat like windows was pointed the finger at 25 years ago.

User info and authentication hasn't been obtained directly from /etc/passwd(etc) since Unix System V Release 4 in *1988*, instead proxying through the libc's NSS to allow for NIS and other directory services to be transparently used. This was later augmented by PAM (1996) and SSSD (mid-late 2000s), which in turn could be plugged into countless other user authentiction/directory services.

"KISS" ended nearly 40 years ago, out of the necessity of working in the real world.

> And what's the next step ? Drop support for /etc/passwd and /etc/shadow

Lots of places already did. Did you ever try to edit /etc/passwd when the name displayed by your company's Active Directory server was wrong?

systemd's user info server isn't yet another huge thing you need tooling for. It's mainly an aggregator. You can plug a parser for /etc/passwd+shadow into it, or AD, or whichever other service you want. It's a protocol, not an API or (worse) a file format from the 70s/90s that can't evolve and can't be extended. There's strict separation of concerns (in contrast to libpam and related ugliness).

If your expectation is that you can look up a user in /etc/passwd then that hasn't been true for decades - even if we choose to ignore NIS as a Sun special, Project Athena had come up with Hesiod in the 80s, and modern enterprise environments are almost certainly using some form of LDAP (either natively or via Active Directory). At some point it becomes necessary to consider whether continuing to apply bodges on top of the existing infrastructure ("Your password is here, unless it isn't, in which case you need to know which backend to query to find it") is genuinely simpler than replacing it with unified tooling that caters to the modern world rather than one which envisaged managing hostnames by just having people mail out updates to /etc/hosts

I vaguely remember some distributions dropping /etc/passwd. The replacement was a directory tree somewhere in /etc, each user-representing directory owned by that user. Inside were files for metadata like real name, a symlink to the shell etc.

I can't find it now, but Openwall's TCB (https://www.openwall.com/tcb/) looks similar. Or maybe that was something from GoboLinux? Or maybe T2 SDE? Nevertheless, life without /etc/{passwd,shadow} is possible and even quite pleasant.