With regard to supercaps, again, the battery technology is advancing on how quickly it can take a charge. The supercaps will take doses faster, so we do build hybrid buses with the ultra-caps.
I think the battery technology will catch up enough that you'll be able to fit in a rapid charge within the window you need to be able to do that—and recover all of your energy from regenerative breaking with batteries—at some point in the very near future.