I dont see it as a way to be mobile but it does have a place as a form of housing. IF you actually look at what is necessary to live vs what we want to live in it could be a huge savings in building costs and energy use. If you are not into small space living it will never work for you. If you want to have a minimalist lifestyle it's perfect.
The issues like building code minimum size requirements need to be addressed. One of the basics of most building code is the issue of size being adequate to not use the kitchen sink to wash after using the bathroom etc. The bathroom has to have a sink of it's own. Windows need to be a certain distance from appliance vents etc. This part of the code is good but mandatory minimums are outdated. In my area 600 sq feet is the minimum building size. A perfectly livable area could be built in a much smaller area than that and still be safe.
Not to get political but when you are faced with the present economic conditions it makes a lot of sense to change the building code to allow for the building of safe yet much smaller living structures. You or I may not want it but it is a viable option for those on lesser incomes. An RV is very bad at being energy efficient. A very small home with high R values and efficient appliances and solar exposure would be very green compared to an RV.
The time is now but you are up against a system that does not want efficiency. They want consumption. Compare all the costs of permits and building plan costs of 300 sq ft vs 3000 sq ft. The code offices are staffed with ex tradesmen and contractors. Do they want a 300 sq ft plan on their desk or 3,000 sq ft? It's also taxed on sq footage.
Any one who can snowbird or full time can surely side with the concept of highly efficient small home living.