The 1954 definition can be applied cross-culturally. It doesn't define 'what folk is' but describes the processes by which folk music - in its myriad forms - has evolved.

Sinister Supporter's definition - 'folk is flotsam' - apparently describes what goes on in many English folk clubs. Would 'folk is flotsam' work as a definition outside this specific context? If you visited a country and failed to find a folk club that resembles yours, would you conclude that said country has no folk music?

If you want to update the accepted definition of folk music, you're going to have to do better than (I paraphrase) - "Folk is anything that washes up on the shore of my club."