Why would google put Youtube sidebar (pop up) on Google+?

Because it is logical. Youtube has many great content. I love watching CN Blue video on it all the times.

Why does it feel awkward?

Awkward? How? You mean the pop up window? Because making the Youtube sidebar reside in G+ page would take space. It’s logical.

Will other button from Google product catalog follow suit?

Obviously. Perhaps. Aside from Youtube? Blogger?

Are you sure?

What? Why looking at me like that? Do I look like Vic?