idiot-proofed derailleurs

. this idea might actually be worth it for a velomobile,
where stalling on a forgotten downshift
can represent a non-trivial traffic impediment
due to the velo' being wider than your ordinary bike
and not easily push-started .]

4.23(2009): tech.gear/mobi/derailleur changing while still:
. did anyone try a front derailer on the underside,
one that would change gears by pedaling backwards?
. that idea would work for the rear derailer too,
but there are so many of those to do,
pedaling backwards would be an annoyance .
. these would be great for when being
caught by surprise in high gear,
and then no longer would you have to find some manual way
of getting started before you can downshift .