Well, do they charge a lot faster than a lead acid battery?
In the limit, sure, they'll charge "instantly", but only if the charger can deliver almost infinite current. That means big diameter wires, and breakers that don't trip.
And that would be something like 2.0 gauge cable coming back from the vehicle's motor/alternator?
Yes, I would think they could be charged more quickly than a lead acid battery. Most batteries don’t like being flash-charged—there’s a loss of energy, and stress on the plate structure. Would it be a good combination? It might well be.
But, it’s hard to beat a man at his own game—I think battery designers may have thought of this. Maybe they don’t consider the super-cap technology mature enough. Maybe there’s another issue. Battery design is its own specialty.