Ya, I think systemd has something like that... Seems like an impossible problem since lower layers shouldn't be parsing higher layer conf files...
Um... we are talking about system, here. However, IIRC, you had to enumerate the ports yourself in /etc/default/portreserve or something like that.
I guess I'll hit the systemd docs, if they exist, about this feature, to see if that could do it for me. However, I'm glad I also have my other workaround as I don't trust systemd not to mess up their feature (change syntax, semantics, etc) in the future as they've done to me sooooo many times.
Welcome to Windows :-). (Feel free to switch to *BSD, although maybe not FreeBSD since they're in the middle of completely reorganizing their init system, too...)
-Adam