Yes, I've seen that definition before and I still don't agree with the implication that there will be no new traditional music in the future.

(a) digital archiving
You may as well say traditional passing on of songs by word of mouth died when the first broadside was printed. And though I can access 1000000 tunes on the net, I still get the motivation to learn one because I've heard someone play it - then I might use John Chambers' tunefinder to get hold of a copy, which speeds the process up a bit, but I didn't know I could do that I would have written it down instead.

(b) Writing 'in the tradition' and resistering with MCPS/PRS
Doesn't stop anyone else performing them, and doesn't stop a song from evolving and changing. Which part of the process of "tradition" is affected by PRS registration? And eventually the copyright expires...

(c) population mobility, cross cultural influence and collaboration...
That has always happened in all the arts. It can happen faster now, but not all that much faster because it takes a while for people's tastes to change and be re-educated. And people still don't move all that much!

Anahata