Yeah, if you're thinking of making affordable electric cars, your way certain would be the cheapest way. However, think of all the labor necessary to retrofit a car, not sure if we can reach any significant mass volume with just hobbyists doing it in their garages. If you do build a special factory and plan on doing lots of retrofitting on Taurus, then I guess another issue would be all of a sudden Taurus used car prices would probably then shoot up?
I think unless perhaps if someday we can develop better in-wheel motors. Then the conversion would be piece of cake... just a matter of swapping out wheels. That'd instantly transform any vehicle into a hybrid/electric car without doing much retrofitting... and just stuff the batteries in the trunk...
Anyway, I guess my dream is that we can customize our cars based on variety of on the shelf parts as much as possible. Be able to pick and choose the best parts out of different companies. Kinda like PCs where you can just add on whatever CPU, memory, graphics card, HD, etc... in order to build your own dream machine. However, unlike PCs, vehicle chassis' not going to drastically improve in performance by that much over the years. It's just a piece of structure... unlike a PC's motherboard. Unless I crash it, I can pretty much stick with a single 'chassis' for the rest of my life and just trade-in and upgrade engines and whatever other parts in order to improve my cars performance... whether you want it to be fast or cheap or green.
I wonder how much would a Tesla S cost if we could put regular gas engine in there. Surely not $100k? And whatever IC engine you put in there, surely it'll perform better and more efficient considering how light and aero-dynamic the vehicle chassis is.
Currently IC engines are still king, but we are branching out... still not sure which way we're gonna go. Are we really going full electric? Or perhaps hydrogen fuel cell? Or who knows what else. This is another reason why I think it's important for cars of the future to be more customizable.