There are extremely few use cases where your app may want to integrate with systemd. Out of those, you get again a small percentage that can't be trivially made

There are extremely few use cases where your app may want to integrate with systemd. Out of those, you get again a small percentage that can't be trivially made optional. (99.9% is just optional notification and socket passing) Outside of large projects which are interested in full system integration like gnome, nobody breaks apps to not work without systemd.