I have been thinking about this a lot (with 2 project cars to complete). My kids would like to get the cars eventually. My gut feel is most running classics will be converted to electric as more and easier conversions are available. ICON has already started doing this and the some of the major Auto companies are announcing kits:
https://www.electrive.com/2020/11/02...onversion-kit/
So my plan is to complete the projects with gas engines and convert to electric later when battery tech get smaller. Right now its the batteries that are the key factor. They are too large to fit most classics. When they start getting smaller and more modular, they will work well in place of gas tanks.
Electric conversions will work very similar to the EFI route. Remember when EFI were bricked by the dealer and you had to go to the dealer for every change. Now there are paths to modify the cars computer available to hobbyists and plug and play EFI systems that retrofit to older engines.
I think the biggest market will be for RV conversions. That is a huge market waiting for the right guy (come on Elon!) to produce. Just think, RVs are perfect for EV! Small amount of daily traffic, huge roof for flexible solar cells, overnight parking in camp grounds with electric, etc. I think the Tesla Semi RV conversions will be a business to get into! Those are my .02