It is possible that using DNS to implement some part of URN -> URL
resolution can be made to work, but not if you tie the ownership of
URN name entry to the ownership of the locations that go with it.
I'm worried a bit about authority in these URN resolution schemes;
you'd like the URN to be secure (in that someone couldn't spoof
urn:/us/government/whitehouse/speeches/clinton/9-10-93/a and supplant
it with some other document).
I don't think we've yet addressed the security aspects of URNs,
although I believe there ARE security requirements.