Teensy 2.0 ++ can be multiplexed and with less than 7 pins have 48 I/Os
Why should my build be filmsy? With the correct tool, hardware and design it can be solid as a rock, just look at the Midifighter.
It's not my first time building something, and as a FB page says.. "Trust me, I'm an engineering.."
I'm pretty optimistic for this build, and I think it could work just fine (I'm just building a prototype, if it works I can get some PCB made in China, buy tons of hardware and start building many more of this things...)
Right now I'm on a R&D status, so I can build it later.