You want the page down key to move you in small chunks. I think this is more of a technique. It's also being done already. Hard for streaming. I think TV's point is that acceleration is just a convenience.
Deceleration is different.
More likely that people with learning disabilities could use slower audio. Also some users with blindness. Change language of 4.11 to refer only to deceleration of audio. Usually Helper App or OS will be doing the rendering. Note that 4.7 could have captions.