Will - and by extension Rob - you two sum up the situation pretty well. One could also include our parents, aunts, uncles here - what, if anything, did they sing to us when we were kids? 'Folksongs'??? Or songs from rambling/climbing club outings, popular films of the time etc.? Some of these songs may have stuck in our memories, some we may even sing irrespective of whether we know who composed them or not, or some we've even possibly used as vehicles for completely new songs. Only time will tell whether anything like 'folkmusic' will be played and sung in 2112, and the same goes for songs crossing over from one genre to another. (It's 'folk' Jim, but not as we know it!) Since none of those pontificating here in this thread are going to be around in 2112, surely the question is really only one of academic interest.
"Fixin' to Die Rag" may be superficially about Viet-Nam, but surely it's the general sentiment of the song - war and the behaviour of politicians and military - that matters?