If Bruce is enjoying the process and experimenting, and the cash isn't a terrible dent, this at least sounds like an interesting project.
Though, as mentioned in last thread, though 3D printing might work for prototypes, would not 3D milling end up being a more durable way to go about it? Not at all an engineering guy, but my impression is that 3D printers take specific (and a limited range of) printing plastics, while with 3D milling you could get a block of Delrin or whatever plastic composition you like, and have a 3D mill carve out the bits.
My initial concern would be the reeds: are you considering hybrid (accordion) reeds for the long-term plans? If not, again a lot of very smart folks have tried to figure out a way to mass-produce concertina reeds, but between methods and scale nobody's had a plausible solution yet. I personally don't doubt someone will eventually solve that riddle; if nothing else when we have really good 3D scanners that can get tons of tiny nuances right, CAD out existing reeds, and auto-mill them, but even those would take a lot of skilled labor to tune. Unless, of course, 3D scanning becomes so precise that a fully pre-tuned reed/shoe can be dropped into perfectly formed chamber. But in whatever case, affordable concertina reeds don't sound to be on the 3-5 year (or maybe even 10 year) horizon.
Not to beat a dead horse, but I'm still of the belief that if we're mass-producing affordable concertina options, MIDI is a way to go. And as conzertino notes, Hayden is arguably an easier MIDI sell as being less tied to tradition than English or Anglo, lacking the available/affordable vintage market, etc. MIDI avoids all the reed issues, opens up a lot of neat modern options for interface, etc.
I would like to see an increase in quality-yet-affordability of Chinese models though. The Chinese make those little 7-button melodeons (button accordions) which are suprisingly okay for $20-30, and with $100 of reedwork are actually pretty decent. If the Chinese made something parallel to those, rather than those huge celluloid monstrosities of 20b Anglos they make, that would also be a step forward for the concertina community.
All that aside, if you're having fun designing and aren't blowing the rent money, I don't see it as being any more directionless than any number of hobbies. I've never understood the whole "building a ship in a bottle" thing, and being able to replace any part of a concertina seems a valid hobby endeavor.