Jan - did you know that Mike Dabrowski can get 25+ miles using an Etek at 48V to push his Honda Insight - probably 3-4x heavier than this bike. (Granted this is at about 30 mph.) http://www.99mpg.com/TheBestHybridmix/
Yeah they have a lot of power but they will not last too long - brushes and lots of cooling required which are wear and inefficiency problems you don't want in a car. If you look at the battery energy calculate the kwh of the pack - in my eCycle powered scooter with lossy 10 inch tires I get about 20-25 miles per kwh of energy. Cars should get about 1/4 that distance on a kwh of energy. Another problem with NiMh batteries is their inefficiency and self discharge - charge them too much and they cook reverse charge from over discharge and they loose a lot of capacity and the bigger the back the more energy you loose - get a couple of kwh of battery and you have to loose more energy that you can imagine. The implimention of the 5th wheel is nice and I thought about doing exactly the same thing in my xB since I have room in back. You don't want to be putting a tranmission on an electric motor if you don't have to because it just adds losses - usually a single reduction with a gates belt or chain is preferred. A hot setup would be a solid slot double stack eCycle rated for 400 amps continuous with maybe the water cooled option to really allow you to push it but air cooling should work just fine. Another thing is to do the math on the life of the batteries and the gains and pretty quick you will find that it doesn't pay.
That is f'in awesome, and implies that an electricified velomobile could weight less, have better acceleration, and much better range with the same setup.
NOW you have the right idea - really slick aero and a 1 seater with 2/3 wheels plus you invest in a good quantity of Li-Ion cells and the thing would have a range of 100+ miles easy and still be light and the cycle count would be way up there better than lead.