After reading all of the above, I've come up with an entirely new "What Is Folk" definition ~ one good enough, at least, for my own purposes:

If the people of a given community share knowledge of a song and can sing along, it's folk music ~ at least for those folk. In the world I live in, this would include Beatles songs and rock 'n' roll "golden oldies" as well as stuff like "Li'l Liza Jane" and "Down By the Riverside"; in your social circle, an entirely different set of songs might comprise your shared tradition.

If a song is newly written, and performed for a silently listening audience, it ain't folk because it is not part of anyone's tradition ~ at least not yet. If such a song catches on, either locally and/or "underground" via word-of-mouth, or in the context of a wider commercial world, it may eventually become part of some community's "folk" tradition.

I think the above distinction is more pertinent than whether the intrumentaiton is acoustic or electric, whether the subject matter is introspective or narrative, or anything else.

Now, as to the argument whether the current musical product of Nashville's Music Row is anywhere near as good as it once was ~ that's just a matter of individual taste. I agree that most of it is pretty distasteful, and therefore don't listen to it.

What I do listen to, almost exclusively, is New Orleans music: jazz, pop-standards, and R&B (real rhythm and blues, that is, not "contemporary urban" sythesizer pop). Our brass bands, for example, share a "traditional" repertoire with which every good player is familiar, which is necessary because individual musicians must be able to play in various different combinations on short notice. Much of the material is indeed "traditional" is the sense of being time-tested, even ancient, but some of the songs and tunes that have become part of this canon are of recent origin. Such new compositions (e.g., Rebirth's "Do Whatcha Wanna") seem to become "traditional" by consensus, just because everyone likes them and enjoys playing them. I'm sure that the same process applies within other traditions, including the acoustic-string-instrument-plus-vocal genre that most of us call "folk music."