I've often wondered if youtube should abandon the fight and allow for portrait videos. After all, a lot of viewers are probably on mobile where they'd rather view it in portrait orientation anyway.
Periscope https://www.periscope.tv/
Also, the web interface could rearrange itself to better fit the description, comments, and related videos to the right of the video if the video is portrait instead of black bars. I don't want to have to go full screen just to be able to see what is happening.
Finally, taking a 1080x1920 video and fitting it to 1920x1080 means that there's a loss of data.
http://thenextweb.com/apps/2015/07/22/you-can-now-watch-vert...