I've been reading San Antonio Rose: The Life and Music of Bob Wills by Charles R. Townsend, published in 1976. It's an excellent biography, which Townsend began researching in the late '60s, interviewing Bob Wills, his wife Betty, and many of the musicians who played in his band. The book is out of print, but the Tulsa library system has several circulating copies.

In a chapter about Wills's 1968 induction into the Country Music Hall of Fame, Townsend asks whether his music really belongs in the country category, and on p. 285 he includes this prescient aside:

Mainstream country music has remained relatively close to its rural and folk origins -- and if this ever ceases to be the case, the term country music will become a meaningless commercial hybrid.