Nice! Having just rewired a 98-key with a microcontroller that only barely had enough keys (and then an 83 that still needed some contortions), tracking down an MCU with enough pins to do a clean matrix was a very good idea.
I know it's controversial in some quarters, but would you consider retrobright on your spacebar and top case?
Lastly, what technique did you use on the insulation on your matrix? I find managing the insulation is the most tedious part of a handwire, trying to trim in the right places, slide it back and forth, burning it off when necessary, etc. All very annoying. I'm thinking of just using bare bus wire and heatshrink for my next project.