Haha, you said BAZINGA!!Sorry but i don't really see a down side.
i.e Both person A and person B buy frame X but person A wants a 64 degree head angle and person B wants 65.... now they can both get what they want.
Or if they both like the same frame and the same headangle but have forks with a big difference in axle to crown...BAZINGA! they're both still happy.
P.S I'm still guessing that these yet to be released Cane Creek headsets have a trick or two up their sleeves
And yes I agree, cos you and I are about the same size and height, yet want rather different size and geometry bikes, this system would allow us to own the same model bike (albeit in different sizes!) yet set it up to our geometric preference.