1 Did the Appalachians not do this themselves?

2 Interesting crossover since the banjo is said to derive from African instruments via enslaved people

3 What evidence is there that Sharp noticed Banjo tunings? I am fascinated.

4 I suppose that Sharp's view would be that you had to use chords built on the notes of whichever scale your melody was based on? Should I think this through in terms of normal tunings mode by mode? Haven't got very far yet. Starting with triads and D Mixolydian; same notes as D Major except a c natural.

I chord D major; II chord E minor; III chord F# dim…?;   lV G Maj; V Am; VI B minor; VII C major. Doable in normal tuning?