mmking:
dougp, can you think of a medium that might work better than Velostat? I've only leant that way because I could basically put the 2 layers together without having to worry about any kind of spacer and rely on the impact to change the resistance compared to the baseline.
It's only a vague concept but I was thinking something like the flat flexible ribbon cable you might see on a printer carriage. I don't know if you can get that without insulation but if not, you could (tediously) scrape away the insulation at certain points and then the impact would press two intersecting wires together. I picture also a sheet of insulating material to keep the contacts apart when the impact pressure subsides.
Another path could be to etch a circuit board with the matrix and place switches over two intersections. Think of your TV remote keypad supersized. I wonder if anybody still make cricket switches?