Probably not, the toes really aren't built for fine motor action the way the fingers are. You would probably get RSI pretty quickly. You'd want to stick to motions that are more typical, such as stepping the foot.

That makes me think of motorcycle foot levers, where the back of your foot is supported by and pivots around a peg, allowing you to comfortable and quickly push the lever down.

hm. Yes, and with a pretty significant (by keyboard button standards) amount of pressure required.

Actually, in a situation where I can't require significant force, the 'upshift' almost seems like it would be more comfortable.

As a motorcycle rider, I'd prefer upshifting all day to downshifting all day.

What if we mount a foot switch upside down above our toes so we just flip our feet up and hit the switch? + sticky keys on the foot switch modifiers

The answer is a keyboard for your toes