I expect that in time, that’s exactly what will happen. Some instance somewhere will offer guaranteed availability and performance for a monthly fee to it’s members. That feels icky at first blush, but why should it? It’s not everyone’s cup of tea, but no one is forced to use that instance to be part of the larger community, and one instance can’t hold the community hostage like a single company social media company could. They’ll have success right up until they don’t and the Fediverse will sort it out through migrations of users and communities.