I have game servers running in house that my daughter and I used. Looking at them we typically only connect to one at a time. So they don't need to be running 24/7.

Was wondering if there was a way to trigger systemd on connection similar to xinitd does things. That way I could have the server shutdown if no one is online for a while... then have it start when there's some attempt to connect.

Realize there's other issues as things like minecraft want to ping the server but just working on the systemd angle at the moment.

Anyone have any examples where they have done something similar?

If your daughter is of game playing age, I hope game servers are but a small part of an active family life you and she share together.

That priority stated, sysvinit or systemd - it's very much either/or, and your distro made that choice of the init system. I would leave init out of it, and use suspend --> hibernate, each with 'wake on lan' enabled, and see how that works out. I wouldn't waste time on this - you don't get those years back.