The AE associated true pyramids with the rays of the sun, i.e. the sun god RA. The cartouche represents a fundamental change in ideology incorporating RA into its iconography as the primary deity which by extension identifies the pharaoh with RA. If true pyramids=RA and RA=pharaoh I have to wonder if the cartouche itself is symbolic of the pyrmaid building age therefore if in fact Huni, and even Senakht (though I doubt it), were the first to employ the cartouche is it possible this means they were the first to begin the process of converting/building true pyramids?
Just a thought.