It also seems like the first step in the "Okay, we have the basic system that works, lets start knocking off the biggest problems with it." mode that internal combustion cars have been doing for the last 100 years.
Their low voltage also makes them hard to use; you need to balance them, and their capacitances vary considerably. Most range from -20/+80% to -10/+20%, but I guess big customers have options to deal with that. Still, if your battery pack is 300+V, and your supercapacitors can only charge to 3V...that seems difficult.
I used to be really bullish on them for regenerative braking - I think some kinds of buses do use them for that - but having tried to use them, I can't see them being robust enough for consumer, and especially consumer automotive, requirements in the immediate future.
Also, it's on the order of 10x the cost for similar capacity to lithium chemistries, and that comes in a package that weighs on the order of 10x as much as a similar battery.
But hey, I'm just a layman. It sounds like you probably know more.
I wonder what life is like for the new employees of elon.
I heard it will not be good.