Maybe not such a large hurdle though. udev was written by Kay mostly and he is on the systemd team. Before udev there was devfsd and hotplug[1], so it's feasible udev could be forked and/or an alternative introduced if it really becomes a burden for distros.
Udev is already forked, in the form of eudev. And Poettering is already having fun taunting them in systemd release notes, with lines like "This is your wakeup call".
Frankly i am reminded of the stuff we would see Jobs pull on stage. Like "Redmond, ready your copying machines"...
[1] http://en.wikipedia.org/wiki/Udev