The pop music of the present will become the "traditional" music of the future. That's how it's always been.

I don't think it's always been like that at all - any more than pop music has always sounded the same. I think all you can say is that some folk songs collected 100 years ago had originally been popular songs (music-hall songs and broadside ballads). Either side of that one period it doesn't work - popular songs from 1750 weren't being labelled as folk songs in 1800, and songs from the 1950s haven't magically become 'traditional' with the passage of time.