I wonder if a meticulously documented "clean room" approach could be used to defeat the named prohibs. It was used in the early days of PC's to produce the first infamous "clones" of the IBM PC's BIOS. Basically, draw up a specs sheet as detailed as one could without providing any drawings, or alternatively provide a manufacturer with a so-called "parts kit" basically all the parts to a firearm except for the receiver, and ask them to build a receiver that would fit all the parts, it <should> not be classifiable as a "variant" since, stictly speaking, an original was <not> used as a basis for a design, but rather is an entirely new design that happens to fit some parts. It's all theoretical of course, but still ... Food for thought.