It's unlikely that there will be any unattributable songs for future generations

It's well known that some songs have already been robustly asserted as traditional when the author was still alive, even to the face of the actual author.

"Attributable", yes, but not everybody bothers. Many will pass in to the body of songs that "everybody knows" or that were learnt from another singer who got it from someone else... and it will take significant academic research to find out who the author was.

Anahata