A port of systemd to FreeBSD won't happen, the amount of Linux-specific functionality that systemd uses makes that a daunting task. And even if somebody were to do the work, Poettering made it very clear that he wouldn't maintain the resulting ifdef mess.
The best thing for the kFreeBSD people to do would be to create their own non-portable init replacement and use all the FreeBSD goodies such as kqueue, jails, capsicum, devd and whatnot. This project should share the portable subset of systemd's interfaces and add its own extensions for kFreeBSD specific functionality. I can't think of another way to bring systemd's advantages to kFreeBSD while retaining an easily understandable and hackable code base. Yes, there'd be some duplication of functionality, but you can't have everything.
Besides, the main obstacle for wide-spread systemd adoption isn't lack of portability but Ubuntu. They are the only distro with a relevant user base that doesn't offer systemd at least as an option.