I think plug-ins will be best for tiny-sub compacts.

#1 if you have a light car, you need fewer horsepower
#2 you need fewer batteries ( fewer kWh )
#3 you can charge with standard 120v AC

The fact is, battery weights, even Li-Ion, add up quickly.
Use the space shuttle as an example. You use 2 million pounds of fuel to carry 7 passengers and 2000 pounds of cargo. At some point, you are adding batteries just for power to carry around the batteries!

Also, you can't get much power out of a standard 120VAC outlet.
With smaller cars, the standard outlet becomes practical.

It takes about 11-12 hours to recharge a 50 mile Plug-in Escape with 120vAC. In other words, it takes many hours of input, for a short amount of output. Look at gas. 5 minutes of input = 500 miles of output.

With small, light cars, we can get close to a 1:1 ratio.
4 hours of charge to 4 hours of drive would be nice.
-John