This exploration of D modal blues is in the style of "Tear My Still House Down". In modern bluegrass and new acoustic music, the modal approach rarely defines the 1 and 5 chord of a tune. It's usually played without the chord note that makes it major or minor. This leaves us with a powerful, mysterious and intriguing sound. There's a reason they're called power chords.
The 4 chord is often defined as major, but not always. Every note that is not in a chord becomes an option for the soloist to explore. The music usually leans to the minor side of things, but it's all open, and it's a heck of a good time.