@Cloudkid It's something that we almost had a soft test when Reddit went downhill a few months back, if users do scale across different instances the load is lifted the main problem you would have is if Reddit goes down and all the users go to one instance such as Lemmy.world or Lemmy.ml as it would certainly make the Fediverse look bad and crash the servers.
The Server space is already a problem for platforms such as YouTube, Facebook and Reddit but they control it by ads and payments from users such as YouTube Premium on YouTube. Main Instances of each platform may have to take up the Ads system if donations don't come in or it may have to become easier for users to create their own website. I read a good article earlier today about how there are issues for the Fediverse in the short term but it seems promising if they get solved.