At least with a recent modern distro I can't imagine this to be an
issue.  I expect we could have a kernel build option that removed the
mknod system call and a modern distro wouldn't notice.

A few things beyond named pipes will break. PCMCIA I believe still
depends on ugly mknod hackery of its own. You also need it for some
classes of non detectable device.

Basically though you could.

For migration with direct access to real hardware devices we must treat
it as hardware hotunplug.  There is nothing else we can do.

That is demonstrably false for a shared bus or a network linked device.
Consider a firewire camera wired to two systems at once. Consider SAN
storage.

Alan