Actually one area I have been exploring, just for fun, is alternative approaches to damping reeds inside diatonic harmonicas to get pure sounding, loud overbends.
My Overblow Booster is one way, inspired my Masaru Hashimoto's design for the Suzuki Overdrive. It encloses the reeds in outer comb chambers, which are stopped by the fingers, or the rear hinged Booster Bar. It works well, but I wondered if there were other ways to do the same job without a large rear fixture. I tried a slide to close the apertures, but it didn't seal well. There are other hole-closing possibilities, but sealing is a considerable issue. The Booster Bar gives good sealing and I haven't come up with anything better in that direction for the present.
Henry Bahnson was the first to try try mechanically damping reeds with his Overblow Harp in 1990, using two sliders that moved across the reed slots (see pic). Jim Antaki has a project on the go to offer an updated version of this, the Bahnson II: https://www.turboharp.com/harmonicas_future
I never tried a Bahnson harp so decided to make a version of my own to see how it worked. Hmmm... unsatisfactory, at least in it's basic form. it does the job of damping the reeds, but because they swing through the slot, as the slide moves across it hits the vibrating reed. No harm done to the reed, but there is a undesirable 'clinking' sound that makes the basic design pretty much unusable for nice-sounding music.
I tried a more sophisticated version, where the slide is enclosed in a housing that lifts it away from direct contact with the reedplate and allows for reed swing. This does work as long as the slider has close tolerances in its housing to seal well, but is really complicated to make: about 12 separate parts have to be lasercut or 3d printed, including the button and spring. Though fun to try as a 'proof of concept', I feel it's not a commercial proposition because it would be so expensive to manufacture.
I tried other internal flap damping devices that lowered down onto the reedplate instead of sliding across it, but so far haven't had success with them. Because of the extremely small working space under a harp's coverplates and the ideal of being able to maintain a cup whilst operating the mechanism, it's quite a gnarly problem!
An interesting alternative approach to using finger operation was patented in 2002 by William Vogtman: https://patents.google.com/patent/US20040123721A1/en
He shows a design with flexible coverplates that can be pressed down with the lips onto some internal damper flaps. In the drawings it looks ingenious, but also very complicated! Drawings are one thing, but frankly I doubt it could be made. Just finding a suitable material for the covers that gave sufficient lip support whilst being suitably flexible would be difficult in itself. But it's food for thought...
Maybe these musings will get you thinking too. Once you consider exactly what's required, you'll see getting the blow and draw reeds of a Richter harmonica damped fast and silently is not as simple as it might first appear!
I've given up for a while, but am continuing to mull it over. Just for fun