This is a more sensible design. You can now read comments while you watch a video, which is clearly a more important use-case than browsing a bunch of recommended videos while you watch a video. The comments should scroll independently from the main column though.
I agree with this redesign since it turns the right side of the video into a general social space: chat when it's a live video, comments when it's a normal video.
Related videos, on the other hand, are static and can be easily moved beneath the video.
Or someone will chime in plausibly claiming experience/relevance to the thing discussed and provide some additional interesting information, in the same way we see in comments on HN.
There's a lot of crap too of course, but at least on content that's informational to begin with (not saying memes and music videos) there do exist good comments.