Does it make sense to compare them as the lines between them blur? Absolutely! That's the best time to compare.

And the same is true for DRAM and flash. There have been several moments in time when the tables have tilted where battery backed RAM PCI cards have made sense, or where sticking persistent Optane chips in high speed DRAM slots has.

Indeed, DRAM and Flash have experienced a convergence - in server and mainframe land there is storage-class memory that functions as a cache or LUT between DRAM and Flash.

I believe we are a bit farther from a true hybrid capacitor. As for true hybrid memory I believe the likeliest solution for embedded applications will be one of the different analog in-memory compute techniques currently being iterated on.

Yes because ultimately the goal of capacitor research is to make it more similar to a battery in terms of storage.

And battery research goal is to make them behave more capacitor-like, eventually they will cross their paths.