A Phoronix reader pointed out a mailing list post made by Lennart Poettering that we missed out on at the end of May. The discussion is about a patch for dropping the udev firmware loader. In there it's mentioned that the systemd developers are planning to move udev onto KDBUS as transport, the kernel-based implementation of D-Bus. In moving this, the developers will get rid of userspace-to-userspace Netlink-based transport udev currently utilizes. Lennart wrote, "Unless the systemd-haters prepare another kdbus userspace until then this will effectively also mean that we will not support non-systemd systems with udev anymore starting at that point. Gentoo folks, this is your wakeup call." So using upstream udev will not be supported without using systemd. Lennart called out the Gentoo developers due to their eudev fork of udev.
Samuli Suominen of Gentoo expressed some hesitation about this change, "I'd really hate to be forced to fork (or carry huge patchset) unnecessarily (I'm not a systemd hater, I'm not a eudev lover, I'm simply working on what is provided to me by *you*, udev upstream)." Lennart countered, "Oh god. You know, if you come me like this as blame me that I would 'force' you to do something, then you just piss me off and make me ignore you. Anyway, as soon as kdbus is merged this i how we will maintain udev, you have ample time to figure out some solution that works for you, but we will not support the udev-on-netlink case anymore. I see three options: a) fork things, b) live with systemd, c) if hate systemd that much, but love udev so much, then implement an alternative userspace for kdbus to do initialiuzation/policy/activation. Also note that this will not be a change that is just internal between udev and libudev. We expect that clients will soonishly just start doing normal bus calls to the new udev, like they'd do them to any other system service instead of using libudev. Good luck."
At the moment there's no firm commitment when the KDBUS support will be merged into the mainline Linux kernel, but it's been anticipated for this calendar year.