just thinking (writing?) out loud
maybe a cobbled up foot brake? maybe not for regular use but like an emergency back up. say if you were able to have rear disc brakes and rear calipers and one was hooked up to a brake lever maybe back near the rear axle, like have a bmx peg on one side with the brake set up to use like the rear brake on a motorcycle.
that all sounds too complicated now that i've written it down, but still doable with some thought on it. now i'm thinking about it as a back up brake idea for a gravity bike if i go back to work on it.