'folk must diversify or die'

Er...how exactly? Folk is very clearly founded in the traditions of a particular country, you can't change tradition. It is true that some have sought to use the traditional base as a springboard for a novel approach but much of the (admittedly small) folk fan base like their music unadulterated by attempts to give it greater appeal. If a folk festival feels the need to book mainstream music to pull in the punters then it is a music festival rather than a folk festival. Nothing wrong with that.. I think Jools Holland is a very good musician, but my preferences in music lie elsewhere.