Haven't seen this yet. If the comments on the right could be scrolled while the video remained stationary I would prefer it, but I doubt that it works that way.
I hate the new look. Thankfully, for now closing Firefox and re-opening it, then going back to YouTube I often get the old look back.
I have not seen the new design, so I can't comment. But I don't see anything wrong with the current design. It's like these folks haven't got anything better to do. Yahoo is also planning to soon launch a redesign of Yahoo Finance, it looks like crap! And IMDB recently launched its new design for movie lists, with the horrendous ''continuous scrolling'' feature, so without any pagination. It's like these people are retarded.
I did see the screenshot, but it didn't become clear to me how it works in practice. I think YouTube should rather be focused on making the site less heavy on CPU and RAM. I must say the YouTube smart TV app is pretty good, quite smooth. The only problem is that you can't easily delete multiple items from your watchlist. They also don't allow you to add movies and series to the watchlist, it doesn't make any sense. Like I said, it's like these people are retarded.