Scott James Remnant (scott@ubuntu.com) said: 

On the other hand, they *tend* to be unique for a wide range of systems.
This makes them pretty comparable to LABELs on disks, and we have
a /dev/disk/by-label

Remember that udev already supports symlink stacking, and priorities and
such.

I don't think there's any danger of supporting a /dev/netdev/by-mac by
default, it'll be a benefit to most and those who don't have unique MACs
will just ignore it.

At the moment, we do not appear to get the proper change uevents from things
like 'ip link set dev <foo> address <bar>', so we can't currently maintain
these symlinks.

Bill