Good. I absolutely hate videos that are so low volume that I have to turn Youtube up to 100%, and then adjust volume in Windows too, to hear anything. And then imagine finding one of the louder videos next. I've tried to give people advice on volume levels, but it feels like no one is willing to do it. Hopefully Twitch will do something similar soon, too.
I think that is exactly the motivation: avoiding the random shifts in volume between videos. Pushing back against the loudness war was probably just a bonus. It's like watching a series on TV and then getting blasted with EXTREMELY LOUD COMMERCIAL BREAKS (and they do that shit on purpose too).
Call me cynical, but I immediately thought that formed part of YouTube's motivation for this.