I think the main reason most of the Linux based distros changed to systemd is due to the more systematic way it enables and support containers namespace and related technology (pardon the pun). This is evident by the mass adoption of systemd around 2015 when Docker is getting very popular and also the ability to use systemd-nspawn as a lightweight alternative to LXC (used originally by Docker). Since Shepherd is based on Guile Scheme it should enable more powerful abstraction and control similar to Guix, its related cousin. Guix is becoming more amazing by the day and you can check several of its related presentations at recent FOSDEM 2020 to get the big picture. One of them is "Guix: Unifying provisioning, deployment, and package management in the age of containers"