The 1:1 connection between a timeline and the scroll position is not something you can currently do in Hype, but a way to workaround this is to setup a timeline with ‘steps’ consisting of a series of segments that correspond to the scroll direction and execute an animation based on that direction. You would use regular JavaScript to detect the vertical scroll delta value, and run a timeline forward or backwards based on that returned value. The blog post here outlines this technique:
Using ‘ease-in’ animations when resuming your animation for new ‘steps’ will make this technique more natural-feeling.