> But the Folk Songs of the future are all around us,

Heh heh. So they've been saying.

But let's look back. To the 1920s for example.

That was nearly one hundred years ago. I can't think of even one 1920s pop song that is now a "folk song."

Unless "folk song" now means "very old song you rarely if ever hear anymore."

Which is certainly a possibility.

The last American (non-bawdy) songs to have been subject to many changes in oral tradition seem to be a few from the 1890s (before radio and practically before phonographs):

"John Hardy"
"The Wreck on the C & O Road"
"Stackolee"
"Frankie and Johnny"
"Railroad Bill"
"Mister McKinley" (1901 but what the hell)
   

Probably a handful more.