Scalability. Federation adds overhead that increases as the number of instances increases. It is unclear to me when we will hit a wall but it’s probably not far off.
How will we pay the bills. Some instances get enough donations to pay server costs but none get enough to pay for staff or developers.
Both of those are only really problems if the fediverse grows, which it hasn’t for a while now. But that could change at any moment.
It’s not so much the hair itself as it being a symptom of god knows what else.