A small thing I want to remark is that at that price, a Model 3 costs less than 3x, and has more than 3x the battery capacity.

Considering DC connectors on EVs provide a direct electrical connection to the battery terminal, and the charge-discharge circuitry in residential hybrid solar inverters can handle them just fine (provided it supports the voltage ranges, but people did this).

I think it's an enormous missed opportunity, that the most common charger standards don't support this (CCS2 doesn't, Chademo does, no idea about NACS)

If this was a thing, I think it would completely reshuffle the EV market, I don't know how used residential batteries depreciate, but I doubt they lose more than half of their value in 5 years like EVS do.