If users started to switch to it, how would the primary instance handle that level of traffic?

They can’t. Not without enshittification and monetization. But I suspect that that is their goal. They have no interest in federation, not even on the future roadmap. The developer also stated elsewhere that he won’t support self-hosting officially, and it only became a thing after long back and forth in the community. I already know where that project will go and I don’t like it.