I still like the idea of a range extender. However, the BMW i3 really highlighted the reality of such a situation when inferior equipment and design is used. Some owners would deplete their battery, then try to continue down the road, using the enging/generator combo. What resulted was a top speed of 40mph down the highway, and 60 miles of addl range, ugh. Of course, all it really required was to start the engine well before the battery was depleted.
What's really needed is a "task specific" engine/generator combo. One that is mega-powerful, clean, light. A gas turbine could fill this requirement.
A microturbine with a really high end stator and DSP converter was what I always though would be the ultimate secondary on an EV.
Could theoretically run on anything - gas, diesel, jet a, a still in your backyard.
Air cooled, one moving part, would be awesome maybe a lil loud..