I'd pay money for one of these, if it had the keys which I want, which this one doesn't. I think the trick would be to somehow make it customizable, but I'm not sure the best way to do that. Parametrized PCB design? 3d printing?
I'm not quite sure, but my dream would be smaller buttons, coarsely modelled on the HP48-style keypad. I can't imagine many people share that dream, but I've wanted to make that for a long, long time.
Coincidentally, you get a long ways there by simple adding a Greek keyboard layout. You hit meta-space, and ασδζχψ. meta-space, and back to normal.
Foreign-language keyboard under GNU/Linux also have a layer with many convenient math keys (²·≈·¾ all exist natively in my normal layout).
A smaller win for me would be to simply print all of that on my keycaps.
You should try building one for yourself, I did [1] and it’s easier than you’d think. I made mine just a basic numpad but I really like the idea of turning it into a tool to enter math symbols.. guess I know what my next project is, thanks for the inspiration!
This one is customisable. The firmware uses QMK, so you can remap it however you like. You'd need to make some key label stickers in Inkscape or something if you want the keys to show the characters.
You could go with a streamdeck and make your own set of bindings. Has the advantage that each key on it is a screen, so it can change for context