Hypothesis: Gluten is not necessary for the structure of chiffon cake, and cocoa powder is just an alternative flour; thus it should be possible to create a truly "chocolate" cake by substituting all of the flour for cocoa powder.
Behold the world's first (probably not, but I couldn't find anyone else who had done it) truly chocolate chiffon cake. You might even say it's the most chocolate (although I do have a plan to make it potentially even more chocolate)
It is light and fluffy, and it tastes like chocolate. Texturally, it's almost a bit like an aero bar, in that it melts into chocolate in your mouth when you eat it. Yet it is soft, and airy, and cake like.