I've been thinking quite a lot about the hi-hat lately.
I don't know exactly how the software will handle it, as I'd like to get a continuous variation of the sound between the closed and open states.
So far I'm investigating the hardware, and it looks like I'll go for an optical detection (phototransistor + led). So, I just bought and tested a KITRONIK 5105 Ambient Light Sensor Breakout Board. It uses a SFH 320-3/4-Z phototransistor, so we're talking about visible light.
The measured response time is about 2 ms, which is probably good enough for a hi-hat pedal. We'll see if it's worth pursuing.