For anyone out of the loop: Custom mechanical keyboard firmware/hardware have been the embedded hobby product of choice for a few years. It's a bit like sneakers, mechanical keyboards in general, etc. Or like the test-pattern boats makers create using 3d printers. If someone goes on an OSS embedded space and asks "What should I make to learn", the answer will probably be "a keyboard". My point is: This has a bigger market than you might think!