Treewind, I can't, in all honesty, say that I recognise the scenario that you paint. In the end, any song can be sung unaccompanied and the majority that you'll find people (folk) singing and humming in the street won't be folk songs. Nor do I see much evidence of a continuous oral tradition that will be passing new songs down the generations for some latter day Cecil Sharp to collect in 100 years time. I don't say it doesn't exist at all (I have, on one occasion, had a song that I wrote sung back to me as traditional) but I don't believe it happens as an ongoing process. Most performers learn songs from recordings and/or songbooks and often (unfortunately) try to emulate the style of accompaniment as well as the words and tune. This does not mean that they aren't strong songs that will stand the test of time. In this day and age of mass recording availabke to almost anyone who wishes to use it, copyright, myspace, youtube, and professional folk artists, the word Anon is not one that is generally found with new songs.

Like I said, I don't want to get into the 'what is folk' debate because, in the end, it's what you want it to be, but I do think that many of what are generally classed as pop songs will be around and performed for a damn sight longer than 50 years.