Thank you for the kind words. I did orginally consider using a programmable stream deck, but quickly realized that it would not be sufficient. My requirements were:
1) Over 100 symbols immediately accessible
2) Single-hand use
3) Small size
The elgato stream deck meets some of these requirements, but it would not have been possible to support the amount of symbols I wanted.
I do use an Elgato stream deck for entering Unicode symbols, and I think what's really needed in this space is a cross between a stream deck and the Mathpad: programmable keys with LCD key caps, and some shift keys to increase the number of available symbols. Then it could support configurable symbol sets.