Haven't have the chance the watch the video yet, but...
I once ran a short, impromptu campaign that started out randomly without any preparation*, so we basically improvised the entire world collaboratively going off different people's character concepts and backgrounds to make them fit the world. And it turned out pretty well overall. It took the weight away from me of having to come up with everything out of the blue when we didn't even have a clue what we were gonna play, and it helped us integrate different elements of the world that were necessary for everyone's character concepts to make sense. Someone wanted an African-looking character, so we added an Africa stand-in area to the south. A couple people were playing traditional elves, so we added a huge forest with the dominant elven city to the north, etc. Going through each character then filling in the blanks in between with stuff that randomly occurred to me to make it all fit together.
I would definitely do it again (if I don't have anything specific in mind), as it was a good dynamic that helped players become invested in the world and helped me come up with stuff when drawing a blank and playing randomly out of the blue.
However, ALL of this happened BEFORE play. We established this as everyone was creating their characters and I was trying to come up with an adventure idea in the background, taking notes and stuff. But once play started, the world was set (for the most part) and we went along with whatever was established. Nobody tried to provide additional input during play and I'm not sure I would accept it. I don't like the idea of players inserting random shit into the game world. Doing it collaboratively before hand is a different deal because we're all still trying to establish what the world is about. We could even discuss further stuff after play to continue fleshing out the world. But inserting stuff in the middle of play just seems so "Oh, so random!"
*I basically got a call one day after years of not playing from a friend who wanted to play and introduce his daughters to the hobby, and also had found a bunch of extra people to join.