Except for finishing touches and error checking, Midi controller number 4, v1.0 is finished! This uses a single 40 pin mCU instead of two smaller ones, which made it a challenge to route all the paths in the small space available. It looks promising though.
I just tought of another idea for a dual mCU version though. Perhaps it would be possible to use i2c for communication between the devices? In that case, I would be able to use hardware instead of software-emulated com, but I'm not sure about the speed of the i2c bus. Will have to research this later if I get into trouble running everything on a single mCU (It should not be a problem, but who knows...).
Here is a pic of the new PCB: