For a trigger throttle, I think it's important that the motor power stops immediately when you let off the trigger. At the same time, if you have it dump the capacitor every time you let off, it could be annoying if you let off only for a short time and wanted to go again. You'd have to wait for it to ramp up again.
It should be possible to do both things. Once you get up to speed, if you let off, it could ramp down at a rate roughly equal to how fast the bike slows down. If you hit the trigger quickly enough, the motor would spin up relatively quickly. Ideally, it would sense the speed and come up to match it instantly. If you let off long enough, it would just go back to zero. Anytime you let off, it kills the motor instantly like the ebrake swtich and coasts.
This would be a great project for one of those little Audrio things, but that's kind of overkill. It can be done with analog parts but make take quite a few parts to have all the functions. I'll see if I can come up with something simple, yet still does the desired things. I could use such a thing myself.
"One test is worth a thousand opinions"