I'm a relative newcomer here, but I have noticed that the most commen discussion in this forum is "what is folk music?". Given that there is no consensus on that question, I have a hard time figuring out who should be the gatekeeper, or what his/her criteria should be. It's also worth remembering that today's orthodoxy is yesterday's radicalism, so too much rigidity now will lead to a pretty dismal future. Either this music is alive, or it's dead -- if it's alive, it will grow where it wants and needs to, despite any attemps to stifle its growth.
However, to please those who want to stay close to the original Mudcat concept, I offer my own overplayed favorite: O'Carolan's "Sheebeg and Sheemore" (I'm sure someone can correct my spelling). It's right up there with "Anji" as a tired staple of fingerstyle guitarists everywhere.