Will there be a plan to add something roughly isomorphic to libudev?
Not in the short or medium term. The problem of libudev, and this
is shared by everything from freedesktop.org as well as systemd, is
that its design and structure cannot be achieved without a monolithic
implementation, and are a stealthy way to enforce vendor lock-in.
In other words: if you try to implement something like libudev, you
necessarily end up writing your own udevd, which is a useless pursuit -
and there is no way to make it more modular.
I'm still trying (using systemd as a study case, since I have a lot
more material to work with for the init system than for hotplug
management) to think of a way to provide similar functionality in a
more Unixish fashion, but this is extremely difficult, because the
political agenda is deeply interwoven with the technical aspects, and
disentangling them is nigh impossible.