Currently I have a friend in the process of swapping a Tesla motor setup into a 90s MR2. Haven't seen any updates lately only due to the fact I haven't been on FB in months but I'm positive hes still making progress with it.
https://www.youtube.com/watch?v=0ZFRRCCouU8
I wouldn't be opposed to the idea of doing an electric swap into one of my cars but just not in the market right now for that. Last time I looked into it, it was 5 or so years ago, and we all know how far advances have come since then. So what was viable then, is highly outdated now. As yes, battery technology is the biggest restraint. Not only size and capacity, it's also packaging. When I did look at options, batteries were the typical large car battery shape, a big box. Once aftermarket options open up to where custom batteries could be made, that should spur it on even more. Think about it, a battery in a pre-formed shape to fit in say a fender well, or spare tire well flush. Utilize un-used areas and be able to distribute weight around the car where desired. Just putting a battery box in a trunk or under the hood isnt ideal. Currently its common for enthusiasts to build a muscle car or such by swapping in a custom pre-built chassis. What if, they make replacement chassis that already include a electric drivetrain and floor pan length batteries. You could just drop your body over it and make the needed connections. A quick search online shows that several companies are already taking that approach. Its definitely interesting.