Years ago I learnt about a stock dealing company in my country which was experimenting with pedals for their operators. Sadly, I cant't find a link now. But I found that interesting. Could be useful on certain applications in which users have to quickly respond to unexpected events by switching to particular tasks (without having to search for them through ALT+TABbing). I don't know, just speculating here.

I like it, probably wouldn't use it on Vim, but I see potential in other applications.