Basically, if you're gonna support a frankensystem where packages can either be compiled against one init system / seat manager / udev impl / lots more, or another one, it really helps to have the concept of USE flags, and I don't know what Debian does to try to support "packages depend on systemd, but we also support openrc instead" without USE flags. Maybe "foo-systemd" and "foo-openrc" packages? Sounds terrifying. "Openrc derivative with overridden repos"? Pain².

The Gentoo gui installation ISO uses kde and openrc, and connecting to WiFi to begin installation means using the NM applet. It works quite well, except for the part where kde really wants to encrypt your wifi password with the account keyring, which as a live ISO doesn't exist. (So, routine "fail to store the password and then go back into settings and re-enter the password" on every ISO boot.) But that's not the fault of an init system.

I have no particular idea what Debian might have done there, but generally the preferred alternative to systemd is using elogind anyways. Which should work fine. You could also try speaking to the upstream maintainers of $PACKAGE about using libseat where possible. Gentoo should support any configurations possible upstream, and possibly relevantly, Gentoo will *rebuild* if you change your configuration, not use libsystemd.so compiled binaries on openrc.

I'm not really sure what you mean by that... Switching away from systemd would break KDE? Shouldn't be -- KDE Plasma is packaged by alpine (no systemd option) and supported just fine on Gentoo's openrc profiles.

Also relevant, Gentoo dropped eudev a year and a half ago on the grounds that it serves no purpose given systemd-utils can install standalone udev, and eudev was unmaintained and broken and did not in fact provide the library APIs which software compiled against, due to its being unmaintained:

[gentoo-dev] last rites: sys-fs/eudev - Andreas K. Huettel

(public-inbox.gentoo.org)

Nonetheless, Gentoo still proudly supports non-systemd installs.

eudev exists, at least today, primarily because there's a vocal subset of people who get extremely angry if a package name or file on disk includes the word "systemd" in it, and will not consent to running a udev implementation if any internal filename happens to be /usr/lib/systemd

These people literally configure their package manager to silently delete any files from ANY package matching the glob `*systemd*`. Prank tip: write a program including "systemdetails.py".