I actually do use vim (well, evil mode in Emacs), and I did set up a footswitch and did map it to esc. It was really annoying, for all the reasons OP mentioned. I guess I also didn't realize how much I vary my sitting/standing posture during the day but keeping my foot over that footswitch really didn't work for me. It also felt slower but I'm not sure if I would have gotten used to it, I don't think I even made it a day before i realized this wouldn't work for me.

This was during a strange time when I experimented with like....i wrote some code to recognize chords on a midi controller and map them to key sequences, so like C-major->switch to home desktop. that was kind of funny. The only thing that was even vaguely useful from all these footswitch etc experiments was using grid of drum pads as window management tools. e.g. shortcut to four virtual desktops = top row of four drum pads. But even that I don't actually use.

anyway, ymmv

I also used a foot pedal for a normal toggle and neither as toggle nor as clutch did the trick for me. I wouldn't use it again unless it was attached to my shoe in some way.