Matt Domsch wrote:

Let me also note that we are prepared to have userspace consumers of 
this new character device node.

http://linux.dell.com/wiki/index.php/Oss/libnetdevname

notes how the kernel patch will interact with udev, describes the new
library helper function in libnetdevname, and has patches for 
net-tools, iproute2, and ethtool to make use of the helper function.

As has been noted here, MAC addresses are not necessarily unique to
an interface.

Only in the case of e.g. qemu (virtual hardware), I think.  (Or some
kinds of broken hardware.  Anything not on the udev whitelist from
75-persistent-net-generator.rules.)

The combination of (MAC, ifindex) is not unique, which is what I meant
earlier -- but the setup on the wiki seems to handle this properly.
Assuming there was a /dev/net/by-mac/00:01:02:03:04:05 link, it should
work fine...