It's a little more complicated than this:

• FreeBSD has a port, libudev-devd, which provides the udev API on FreeBSD
  • I don't know how extensive the API is that that library provides, and whether the entire udev backend would work with it
• In packaging, we remove the udev dependency as well as the bits that actually *need* on udev (powerdevilupowerbackend, udevqtclient, and udevqtdevice)

So this code is used, downstream, and I don't think it should be removed like this -- perhaps the udev-is-optional stuff should be merged from downstream instead, and/or the udev support on FreeBSD investigated to find out what it can do.