Not sure if the author's talking about the Regulative Principle hymns of the Reformation, or the latest Word Records "Zoe Girl" release here.
"Reformed folk music" is an incredibly poor phrase to use. What music is being referred to here? Is it the current playlist on K-LOVE? The content of contemporary Christian (rock) music in the last four decades is more Arminian in theology and practice than Reformed. And I'm not aware of any church that uses "folk music" in worship, unless the writer meant music performed on guitars instead of organs? The term "folk music" conjures up memories of acoustic guitars strumming out Joan Baez protest songs, not the electrified Fender Stratocasters performing the latest John Tesh worship song on stage during Sunday Mass.
Sadly, there are great swaths of Catholic parishes here in the West that haven't seen an organ. Ever. Acoustic guitars, on the other hand ....
It's what "everybody wants". Or so the "experts" say.