Many electric motors already use capacitors for startup and burst load events. That's more towards the AC type motors, less towards the DC if I understand it correctly.
I think the most promising thing for electric vehicles is the reduction in the price of LiFeP04 (lithium) battery packs. Their energy output is very linear, it drops very little voltage even when their remaining energy is low. This is a vast improvement over all other battery types for that reason. Also, they lose very little energy as a result of low temperatures. Regular AGM's lose half their energy at half temp, or thereabouts. Lithium's have 4,000 or more cycles whereas AGM's have only 500. Lastly, like a capacitor, lithiums can take as many amps in as they can let out. So, in my electric motorcycle, the batts can dump 275 amps all at once for full throttle. If I wanted to have it charge quickly, I could invest in a 275 amp charger (or even half of that). The bike could be charged in 10 minutes or less with a big charger like that.