Yes, it's an interesting question. Every time I look around more closely at battery tech you see all sorts of things being researched. I expect that the battery tech we are looking at now will both incrementally improve for power density and charging capability but also may be displaced at some stage by significantly different approaches. I don't claim to be an expert though.
As we've discussed before, current charging is remarkably efficient, when slower than filling a tank of gas, so I would guess that the possibility of ultra capacitors becomes more relevant when you are talking about ultra fast charging, where I can imagine the physics for that becomes more challenging and ultra-capacitors could have a role.
There's an article here about full super-capacitor batteries, downside is they go flat if left for longer periods, but allow relatively fast charging.
https://www.theguardian.com/environ...acitors-electric-car-batteries-charging-times
And here, where discharge rates are said to be even more of an issue with some designs.
http://www.hybridcars.com/supercapacitor-breakthrough-allows-electric-vehicle-charging-in-seconds/
A different approach to fast charging here
http://www.batterypoweronline.com/a...ging-can-it-play-a-role-in-the-ev-revolution/
This paper points to a hybrid lithium ultra capacitor approach.
https://www.sciencedirect.com/science/article/pii/S1876610215005809
I think this goes into that last particular battery design solution in more detail, but also indicates that this has been a pretty intense area of research, and is challenging. "High energy and high power electrochemical energy storage devices rely on different fundamental working principles - bulk vs. surface ion diffusion and electron conduction. Meeting both characteristics within a single or a pair of materials has been under intense investigations yet, severely hindered by intrinsic materials limitations. " So while this seems to be one more advanced approach, who knows what else is being pursued.
https://www.nature.com/articles/srep04315
A bit hard to differentiate journalistic simplification and hype from where the most promising real research is going. And always hard to predict winners in technology battles. A google search on "ultra fast ev charging supercapacitors" came up with a lot of hits.
