I can definitely see certain brands doing well with their own forums. Sports teams would be a very good niche for hosting their own instances. Another one would be the entertainment industry. It’s just not feasible for companies that aren’t interesting to talk about. Like there won’t be a Coca-Cola instance worth a lot of users.
If you have a bunch of people guess how many M&M’s are in a jar you can average the guesses and you’ll come very close to the correct amount. A recommendation system can be very democratic in that way. When reddit still had their public API I would take advantage of this fact and use it to decide if something was a “deal” or not on PC parts. I was tracking the prices of computer ram at the time as an experiment. It worked very well. If they are federated properly, then their content can be filtered and appear on an instances front page.