In principle, capacitors can do a few desirable things chemical batteries cannot do. (1) Infinite numbers of charge and discharge cycles without significant degradation. (2) Sustain very high rates of charge and discharge. (3) Provide and allow much higher short-term current flows. (That makes them ideal energy storage candidates for regenerative braking and rapid acceleration).
The only rational automotive applications for them I can envision are in hybrid vehicles that have limited battery range such as Prius. Prius gets good fuel mileage mainly because of its efficient Atkinson cycle gasoline engine, not so much because of its electrical regenerative braking. There is some hypothetical possibility of reducing costs of batteries in all electric hybrid vehicles provided that the batteries don’t have to handle high current loads of regenerative braking or short periods of rapid acceleration. In principle, super capacitors could take the high current loads off the vehicle’s main lithium battery pack. The main battery pack might be made cheaper if it were intended only for relatively low current flows. It’s doubtful that it could be made enough cheaper to offset the extra costs of the super capacitor bank and needed ancillary circuit elements. I can only think the Volvo project is 99% PR bunkum that will never actualize as a consumer product.