"Surely 'folk' as a word has evolved into multiple definitions in different contexts"
How does this help our determining what we mean by folk song Steve?
The sad fact is that we have woefully failed to attract anything resembling a wide following for our music means that the definitions that exist outside the 'folkie greenhouse' are the ones documented and fairly clearly defined.
Abandoning those definitions on behalf of self-interest and ignorance on the basis of what happens in a dwindling number of clubs does nothing to draw in anybody - on the contrary, it adds to the confusion and ignorance.
You're not happy with '54 - fine - give us an alternative we can toss around and see if it fits.   
What you are proposing is moving away from a definition very much in need of repair into an 'anything goes' situation.
Doesn't work for me, I'm afraid.
Jim Carroll