Extremely creative approach to the theme. I dig it! 5 stars.
I do have one little nugget of wisdom that doesn't come from me, but I think it would be well applied to this game, if you work on it more. Paraphrasing here but, "The goal of level design is to give the player an opportunity to use all the game mechanics".
The mechanic is obviously one thing only, but being big feels fast and being small feels nimble so it's kinda 2 mechanics in 1.
However, the levels as they currently generate, don't really allow the player to feel true exhilarating speed (rather, the feeling of crossing vast distances quickly for an extended time). I think it would serve the game well to space out the obstacles so that the feat of getting through a sneaky tunnel or over a nasty hump is rewarded by drifting through larger distances. This could still include some elevation changes, like almost floating down a set of stairs quickly or whatever.
With some visual context added, like a paralaxing landscape background or a cityscape, it would feel great! speed lines, also!
You've got a real gem here, and my suggestions come from a place of love and enthusiasm! This could be the next speedrunners or something. It's got great potential!