Very interesting.
Back to the OPs question, is it not possible to buy and register a vehicle in France as a non-resident? What are people with holiday homes doing for transportation if they are staying the full 90 days at a time?
I too am curious because I am purchasing a vacation home that needs some fixing up and was planning to buy something like a used Berlingo or Kangoo to haul supplies in.
Is the EU law saying I should buy it then register it in the US, then get French liability insurance on it? Or is the law aimed at keeping citizens of one EU country from registering their vehicles in another (possibly cheaper) EU country, and non-EU citizens are another matter completely?