I agree it's probably not so bad even for retrofits - 70% of housing in the US is SFH or a duplex (https://www.infoplease.com/us/census/housing-statistics). Getting a charging solution for those units seems achievable. I'm also willing to bet that multifamily housing is generally massively over represented in blue cities, which might be able to require/incentives retrofits. That's a huge marketable population to start buying electric vehicles and normalize them. I suspect that by the time there is significant used electric market there will also be enough market and political demand to figure out the multi-family situation.