Quoting Steve Litt (slitt@???):

> Wait a minute. This is getting interesting. I seem to hear you saying
> that, until Devuan has vdev, I could replace udev with mdev from
> busybox, but only if I don't use a "full-fledged desktop environment."

The cited folks on the Gentoo wiki, IMO, were erring on the side of
caution, there. I'm guessing that they are vaguely thinking of
DE-oriented applications like KMail that expect to call libudev to
'introspect and enumerate devices on the local system
(https://www.freedesktop.org/software/systemd/man/libudev.html).

Now, personally, I don't give a rat's ass about libudev or its syscalls,
and think any userspace application that requires those is broken by
design -- but the Gentoo wiki people realise some people do like them.

> Can I assume for this email thread that a "desktop environment" is a UI
> that has a distinct part that serves as a window manager? If so, what
> makes a desktop enironment "full-fledged?" Would it be by any chance
> that it gets started up by a display manager, instead of by the startx
> command?

Nope. You're overthinking it. See above.

> You're a server guy, whereas I'm a desktop guy who likes to have his
> underlying operating system built like a server. Given my situation, it
> looks to me like I'd need to just replace udev commands with mdev
> commands in a few rc scripts and init scripts. That sound reasonable?

As Mr. Karl Hammar just got through saying (tack så mycket, herr Hammar),
it's entirely possible you need nothing beyond an old-fashioned static
/dev tree, per se (not counting annoying and spurious package
dependencies that claim software requires udev or libudev even where it
doesn't really). Except for one majorly annoying thing: Xorg packages
have lately been compiled to assume udev support, though reportedly this
too can be worked around by creating the old-school xorg.conf you may
have forgotten used to be routine:
https://unix.stackexchange.com/questions/274149/setting-up-xorg-input-devices-without-udev

I'm not going to make promises, though, about what annoyances you'd
encounter in ditching udev/libudev for mdev or static /dev. That's what
testing is for (e.g., in VirtualBox or similar).

-- 
Cheers,                    Long ago, there lived a creature with a 
Rick Moen                  voice like a vacuum cleaner.  We know little
rick@???        about it, but we do know that it ate cats.
McQ!  (4x80)