Lukasz, I looked at the page from Edward Jay, it is really impressive, interestingly enough I thought If I ever get enough time to work on this I would probably start with a 3D printed model, I looked at the concertinas on his page, they are so cool! I will send him a note to get his feedback on the layout.
Don, I feel that is exactly the reason why I find it most appealing, I don't have an EC unfortunately, but I feel the EC especially allows for simplicity of play for melodies (with a bit of harmony here and there) and maximum portability/range, at the expense of allowing for simultaneous harmony/melody at a larger size/weight and smaller range (duets/anglos). I think nothing comes for free 🙂, but I feel this is a good trade-off and for best simultaneous harmonic/melodic playing I believe the accordion works really well; I have a CBA which I really enjoy (but play badly). Ultimately I think I really should try playing an EC to see how it goes (It's on my wish list / wife disagrees as I have two accordions already 😂).
Yes I find alternative isomorphic layouts really interesting but I know of their fate in history. I limited the project to the Wicki-Hayden layout as it would be most familiar (the idea has been around for a long time 🙂) and (modern) Duet concertinas employ this system; the idea being as these layouts are regular they are much easier to learn.
The hope I had with this project was to document every little step and keep everything open source (perhaps even in a wiki) so that others can reproduce/discuss/contribute to the work if there is value, but let's see.
Thank you for all your comments,