I think I read that one of the BSD variants has adopted it.
FreeBSD adopted it. But FreeBSD is more closely related to Apple than any other system.
But after I have asked and asked the question about why no Linux distro has forked it, all I get is "systemd sucks" type comments, or the chirping of crickets.
When I looked at it, I felt it was insufficient. It is tightly integrated with Apple APIs, and really works well with the Apple system (I do think it's a nice piece of engineering), but I didn't think it would be particularly portable. For example, using it to manage a system like Apache doesn't work as well. I've been wanting to look at FreeBSD's version, to see what changes they made to handle certain use cases, but I haven't had the time. In fact, I am definitely going to put that on my list of things to look at, because it could be really good.
At the same time, there is a long history of every Unix writing their own init system, and every other Unix hating it. In fact, you can omit the word 'init.'