This is an approximation of our current family car:
When we go travelling, we usually need a larger trunk so we have this add-on trunk:
This is a trailer which is about half as long as the car and of the same height and width. It fits everything we need even for a long vacation. Or all our bikes for a shorter one. Or the insanely large family shopping at IKEA. Or ...
So, in our case it almost never happens that we travel far without our trailer attached. So why not use the trailer for the extra engine to boost an electric van? It would reduce the trailers capacity by a little and increase the range of the electric family van by a lot.
For us the combination of an electric car with an add-on range extender would be the best. In the city we charge the car from a wall socket and drive not too much per day. For trips we hook up the trailer which extends both the luggage carrying capacity and the driving range. With this combination we could still pass a good distance on the batteries, e.g. in a electric-only zone.
At the destination of our trip we could again take off the trailer and do short trips purely electrical.
Dear car makers: Start to produce useful and affordable electric cars and I'll be most happy to buy one. Think about modularization and reusablity to go beyond electrifying standard cars.
Update: I just found www.eptender.com who offer a tiny trailer (for small cars) with this idea, which proves that the idea is working :-)