I learned these inversions from Jens Kruger, and they've been really useful in helping me understand 7th chord theory.
In bluegrass, we primarily use triads, or three note chords. Jazz consists mostly of 7th chords, and it's fun to start to incorporate those sounds into your bluegrass playing.
The chords and arpeggios I'm demonstrating are diatonic to G, which means all of the notes I'm playing in the chords and arpeggios are "native" to the key of G. They're all in the G scale - G A B C D E F# G.
Strumming vs. Picking
It's great to learn all of the 4 note chord variations, and that is very useful for strumming in a dixieland jazz or gypsy jazz setting.
Incorporating these chords into a bluegrass setting is interesting. To be able to pick these chords with the 3 fingers we have available, you need to leave one note out.
In each chord, the 3rd string note is the 5th, which is and the weakest note in any chord. That is the one I chose to leave out, which leaves you with a chord using strings 4, 2, and 1.
Coming soon: When and where to put major 7th chords in bluegrass.