I tried installing seatd-runit and it worked out fine. I had to make a small change to get my slim-runit to use seatd, but after that it worked fine.
However, after reboot I saw messages during shutdown about elogind still running. It was started by something at boot.
I could not find any runit startup, but then I tried removing it. I see this
# pacman -R elogind
checking dependencies...
error: failed to prepare transaction (could not satisfy dependencies)
:: removing elogind breaks dependency 'elogind' required by libappindicator-gtk3
:: removing elogind breaks dependency 'elogind' required by networkmanager
:: removing elogind breaks dependency 'elogind' required by polkit
:: removing elogind breaks dependency 'elogind' required by xorg-server
I suppose that means I either have some wrong package installed or I cannot remove elogind fully. I am running this on my rpi4 with armtix and the xorg-server looks like this
# packer -Qi xorg-server
Name : xorg-server
Version : 21.1.1-3.1
Description : Xorg X server
Architecture : aarch64
URL : https://xorg.freedesktop.org
Licenses : custom
Groups : xorg
Provides : X-ABI-VIDEODRV_VERSION=25.2 X-ABI-XINPUT_VERSION=24.4 X-ABI-EXTENSION_VERSION=10.0 x-server
Depends On : libepoxy libxfont2 pixman xorg-server-common libunwind dbus libgl xf86-input-libinput nettle elogind
libpciaccess libdrm libxshmfence libxcvt
Optional Deps : None
Required By : None
Optional For : None
Conflicts With : nvidia-utils<=331.20 glamor-egl xf86-video-modesetting
Replaces : glamor-egl xf86-video-modesetting
Installed Size : 3.54 MiB
Packager : Unknown Packager
Build Date : Tue 23 Nov 2021 02:44:45 GMT
Install Date : Sat 27 Nov 2021 12:17:56 GMT
Install Reason : Explicitly installed
Install Script : Yes
Validated By : SHA-256 Sum
I suppose it might be feasible to provide something in both seatd and elogind provides that would create a solution.
For now I switch back to elogind.