I been thinking about this since you said it. And I do think it's possible to retool it into BM Primal. But it comes down to this question: how much until it becomes more practical to just design a new mold and do it right? We know that after a certain point it becomes cheaper to design a new mold from scratch. I think that may be the case here. New arms from scratch. New legs from scratch. New crotch piece. New robot head. New beast head. With that new beast head comes new back and chest and belly, transformation engineering. What would be left would at most be the basic torso framework. And after all that, it still wouldn't be good/accurate enough to be called Masterpiece. I think there would be more work required to get a "not quite good enough" result than there would be money saved from just making a new one from scratch. If this were a standard $25 voyager toy, I'd say it'd work. But I don't think they could get away with a retool for BM, on the Masterpiece platform.
You have given this far too much thought. Glad I could provide entertainment for your Sunday. ;-)
But you make a fair point. My only question would be, given the shift to doing everything in CAD, whether basing it on the same skeleton structure would still save money, because at least they've already worked out the transformation scheme? (Genuine question - I have no idea how this works.)