Hi Frank and Hans,
The requestAnimationFrame is actually good.
You can even move the script in the header. It loads the CSS async and doesn't block render.
The advantage is that it - if put in the head - it loads earlier than the present Autoptimize code. The current code first waits for page load and then sends a request to the server for the CSS file. RequestAnimationFrame loads it much earlier.
As far as I can see it will just involve a minor change in Autoptimize code to include it.