@Chagall mr. Grell named as biggest disadvantages of planar weight and "home listening" ( I think he was saying about fragility).
And when he was talking about possibility of limits of dynamic drivers he said primarily about efficiency and weight.
As for his point of view about problems of manufacturing dynamic drivers.. I think I can produce mediocre sounding dynamic driver during an hour on youtube stream including winding my own coil. Why I'm so sure? Cause I've made a lot of dynamic drivers in my life

And I even made a hybrid of dynamic and planar.