Interesting idea Ian - have always believed that folk music has been underused, undersold and misrepresented when it comes to films - notable exceptions of course; John Tams' excellent contribution to the beautiful St Kilda film. 'Ill Fares The Land' springs to mind.
Not to throw cold water on your suggestion - wonder how you feel about moves by IMRO (Irish Musical Rights Organisation) to claim payment from every cinema throughout Ireland for EVERY TIME a piece of music is played in a film.
Jim Carroll