A 4th wheel
Actually I'm being serious! As an additional model in the range, I've always thought that a pair of cycle winged rear wheels would look brilliant on the Three Wheeler. That and a pair of pukka Brooklands exhausts.
That would be a 2/4 then?
Seriously though a 4 wheel version of the M3W would be the perfect entry level Morgan but I fear meeting car, rather than bike type approval regs would kill the idea.
BUT a kit car based on the M3W could work.