SuperCapacitors have a place in the near term future. They are not "premium" nor "special high-end yada yada" nor expensive.
Their mission on any vehicle is to add flexibility and reduce fluctuations caused by various factors.
There are two main advantages supercap bank gives:
a) extreme regen acceptance with unlimited cycle count and no degradation - especially useful for heavy duty hybrid transportation (relatively small li-ion pack is unable to accept that much energy while slowing down heavy vehicle)
b) extreme power output - again, works well for heavy transportation that needs short-term boosts during acceleration, but also sport-cars. Either electric or hybrid vehicles will give excellent results with supercap bank. Li-ion battery pack that can handle half a megawatt of output power weight a lot (100kWh pack). But a supercap - 30-40kg - light as feather. Though it takes some space, supercars care little. It's not a problem to reduce rear seats from "midget" down to "Barbie doll".
And some secondary advantages - readiness in extreme environment - very cold, very hot. Regen when battery full. Regen when battery cold. Raise vehicle efficiency (more efficient regen and acceleration). Different battery (less output power, more capacity) possible.
There will be no supercapacitor only EV in near future - downside of capacitors, ironically, is capacity. 1kWh of energy weighs 150kg as of right now (6x worse than lead acid). Unlikely it will ever catch up with chemical battery, as these also get better.