I think that's a bad idea for a couple of reasons.
The people involved in these things that are most prone to instigating violence are already prepared for less-lethal deterrents. They have respirators and goggles.
A common weapon at these incidents is a 'smasher', a long pole, often disguised as a flag or sign, with a length of chain with a padlock attached on the end. I think you'd have a really difficult time successfully attacking people with pepper spray without risking one of those upside your head.
If you fog out an area with bear spray you're likely going to catch some yourself. This isn't a huge problem if you're deterring a problem bear, you have other concerns, but it could be a problem if you're going to transition to lethal force on a crowd. I did some minor testing of this back when my plan was bear spray then gun, and it's doable but far from ideal and wouldn't work when identifying multiple targets quickly.