I just signed up for Prime here and finding that I could not natively watch videos on 2x is nearly a show stopper for me. :(
I watch all farsight youtube videos on 2x since they are not so word dense as the remote viewers spend half the time finding words and not talking. After a bit of playing around I found this Google Chrome extension that actually worked.
After installing the extension, reload video page and a control overlay will appear on the top left of video where you can click + to speed up video. You need to hover mouse in top left corner for the controls to show. The extension has a few options you can set as well.
To many videos here to watch at 1x
I would never get through them. Not enough time. Now that we have 2x, I might have a chance. :)