So long as instances are serving content from other instances (pretty much required for a social network), there will be demand to be able to block other instan

So long as instances are serving content from other instances (pretty much required for a social network), there will be demand to be able to block other instances. Of course, people could just host their own instance, which is possible with Mastodon, and is indeed what a lot of people already do. Mastodon uses the ActivityPub protocol, and there are other implementations that use this protocol (Pleroma, for example).