It’s great to have your words Eric! Thank you.
Here is the link to Eric’s “Why” of instruments. A joyful and informative read, I highly recommend : https://www.landscape.fm/why 
About the look of an instrument, I totally agree with “implications of the external design on the internal design”. And there is a trend to simplify the look.
Much like architecture, the form of musical instrument has gone through the Classical and Modernist era, which seems to be an inevitable pattern as technology rises. Decoration in the form of luxury materials and fine carvings, are gradually replaced by useable elements and ergonomic layout.
We still favor decorations, but they has to be functional, logical, clean and frugal. ENIG is preferred over HASL, not just for its golden look, but also corrosion resistance, long life and a flat surface. LEDs are very welcomed as long as they indicate signals, events or states. Rectangles are more appreciated than other shapes, for the efficiency in production and the use of space.
I guess it’s also because of the huge amount of freedom we have with technology. As you said, “simplicity and limitations are amazingly freeing”, thus we are self-disciplined with a technological principle, practicing minimalistic approach in designs.
Your last chapter about meditative value is both poetic and practical. Under the obvious and concrete need of sound and functions, there is always a wish for time of immersion while we choose an instrument.