The reason Gentoo forked udev is that they have a commitment to user choice. That is, you as the user gets to decide everything. If you want to use udev, fine, if you want something else, also fine.
So they created eudev because it was becoming more and more of a hassle to dig udev out of systemd for use with non-systemd installs.
And i think LFS has also adopted eudev for their "traditional" book now, because they ran into the same issue.
Something like this should really give pause for thought in the "init" debates, as it is a stark reminder that systemd has gone far beyond being just about init. And thus all those videos demoing systemd vs "random init of the day" boot times end up being a distraction rather than enlightening.