This is a minimal pacman package that pretends to provide systemd, systemd-libs and libsystemd.so=0-64 functionality and creates the symlink /usr/lib/libsystemd.so.0 which points to /usr/lib/libelogind.so.0 to solve dependency issues and prevent some packages like seatd from crashing when trying to use a distribution shipping makepkg and SystemD, without SystemD.
git clone https://github.com/Secondarian/archlinux-systemd-stub
cd archlinux-systemd-stub
makepkg -si
I personally use this so that I can have the x86_64-v3-optimised ALHP and CachyOS repos above the Artix repos in /etc/pacman.conf without switching to SystemD and I don't know of any other practical use case.
This has only been tested by me on my fairly minimal system, issues may arise on more bloated environments like systems with full desktop environments because these may have some more SystemD dependencies.
If pacman asks you to replace you standalone udev package with systemd on every single update, uncomment IgnorePkg in /etc/pacman.conf and add systemd to it.