Traditional Folk music hasn't changed, it's roots are traditional and, as such, remain in the age they were created.
The way all modern folk music is shared and saved is a different matter.
It's going to be a lot easier to have a discussion about the music of the 20th century in 100 or 200 years time because it's all still going to be accessible, for better or worse!
Resources like Mudcat are great because they harvest from a huge catchment of people interested to preserve and share musical knowledge that otherwise might be lost, and here on the internet they'll remain for future generations to argue about "What IS Folk Music?"