The pressure sensitivity makes me think pressure sensor and analog input. That in itself makes it more difficult as an ADC is slow compared to a digital input so scanning all those 300 keys may take too long. OTOH solving this would automatically solve "aftertouch" which seems to be basically a pressure sensor.
If double switch for speed detection that'd make for a whole different problem of reading the key press, easier as it's digital, harder as it requires storing the moment the first switch is triggered, and comparing that to the moment the second switch is triggered - maybe just microseconds apart. Won't such keys produce an analog output themselves?