Hopefully now with advances like Suzuki and Easttops octave basses, Tombo and Easttop's pocket basses, Brendan's new slider mouthpiece for the Suzuki and Hohner harps, Low Low harps, and even the Lucky 13 we can see some good low octave work on harmonicas. It seems the potential is there for a skilled player (not me
I've heard haunting Melodies played beautifully on a Cello and Bowed Double Bass.
Yo-Yo Ma did some great work with his Silk Road project. Harmonicas are at least as expressive and could be retuned to make some things flow better. Maybe a diatonic layout ( something like 4 key, or even Paddy Richter) would restrict chromatic playing, but it could increase fluidity and playability.
I took apart a couple of Huang Octave Basses and made a comb for a blow/draw Bass. I left the blow notes as is, but retuned the draw notes in each hole to a semitone flat, except the C and F which I left to allow blow/ draw enharmonics.
I'm still not happy with my valves in the lowest few holes yet.