This is what I did for a daemon I'm maintaining. Type=notify support was requested but I'm really allergic to adding new libs to a project until they really do some heavy lifting and add enough value. I was pleasantly surprised the protocol was that simple and implemented it myself. I think systemd should just provide a simple standalone reference implementation and encourage people to copy it into their project directly. (But maybe they already do, I did that almost a decade ago IIRC when the feature was relatively new.)