What should replace it?
I wish I'd been paying attention while the Systemd Cabal (their phrase, not mine) was canvassing and proselytizing... I had a lot of free time back then and could have spent some of it putting the vast majority of the "missing" features from openrc.
It's somewhat unfortunate that the switch to systemd killed the debian-on-FreeBSD project. Had they chosen openrc, that project would have been able to continue.