In practice I think systemd-udevd probably still runs without systemd, but as I understand it that's not an officially supported solution and the systemd developers have said they reserve the right to make changes that break it at any time. (The main reason why they haven't yet is most likely that their attempts to integrate dbus into the kernel and systemd more tightly were rejected by the kernel devs; if I remember rightly that was expected to be the point at which you could not use it without systemd.)
Using the kernel interfaces that udev relies on without using udev itself is also unsupported and the developers consider it within their rights to break those as well.
It has been supported for at least the last 9 years now, I don't see why they would have any reason to break it.
>The main reason why they haven't yet is most likely that their attempts to integrate dbus into the kernel and systemd more tightly were rejected by the kernel devs; if I remember rightly that was expected to be the point at which you could not use it without systemd.
That seems quite dubious, udev has never depended on dbus, and there really would be no reason for it to ever do that.
>Using the kernel interfaces that udev relies on without using udev itself is also unsupported and the developers consider it within their rights to break those as well.
This I know is true, the netlink stuff varies really wildly from driver to driver. The alternative would be to put udevd and the other userspace bits into the kernel, which I really doubt anyone wants to do.
Using the kernel interfaces that udev relies on without using udev itself is also unsupported and the developers consider it within their rights to break those as well.