Unfortunately Morgan exploited a loophole in US law that allowed a 3 wheel car to be registered as a motorcycle. Some countries, such as Great Britain and Italy, have specific regulations for 3 wheeled vehicles and they are also covered under EU vehicle classification. These rules are now somewhat outdated and were never really intended to apply to vehicles such as the M3W that have car controls. We therefore have a situation in Italy where a bike licence and helmet is required to drive one even though no bike riding skills have any relevance for the M3W. The answer is obviously specific regulations to cover this class of vehicle.
It seems that some states in the USA have realised that the M3W is really much more car than bike and I foresee a general clamp down on the category, unfortunately for US enthusiasts.
Australia seems to have seen the situation reasonably correctly and, despite some ugliness in the solutions adopted (not really the fault of the regulations), I think they have got it right. They seems to have accepted many compromises that would make Australian homologation impossible for a car and have approved the Australian spec M3W a minimalist car with a reduced safety spec by comparison to the 4 wheelers. In effect they have created a precedent for reverse trikes with car controls that could be followed by other manufacturers.
I hope, for the sake of our American cousins, that the legislators in the US are looking at framing specific rules for reverse trikes with car controls. If not I suspect it will become increasingly difficult to put such a vehicle on the road.