Since OpenRC 0.60, user services are now supported: https://wiki.gentoo.org/wiki/OpenRC#User_services. Hence it should be possible to add back the removed OpenRC support.
When I have free time, I intend to take a shot at implementing it. No idea what the implications are yet for timers or other event hooks.
If successful, would a PR be appreciated, or would keeping PSD purely SystemD be preferred?