well I guess with the normal engine it is not for casual user to remove and swap. you need tools and place to work at.
also you need to store it properly where if the engine/batery pack is rented
then it is not of your concern.
but with microturbine design it might be that easy.
I saw reports of new MT that are under 500 lb in weight and the sise of a laguage box. with proper design it might be posible to make a quick connect/disconnect system that would alow most (not all) users to remove it from the car if you wish to do it.but I think most people would just let it ride.
under 500 lb is not a big deal to have a peace of mind.
and no range issues.
I am not pushing the microturbines

but it does make sence.
here is the link to a concept for an in-wheel motor by "Protean???s "
that you can couple with good on board generator
"http://www.smartplanet.com/blog/thinking-tech/innovative-motor-lets-gas-powered-cars-go-electric/6940"