The costs of the servers will crush a lot of instances. I can't imagine the hosting costs the main kbin and lemmy instances have right now, and it'll only go up as people join in. I think we'll see server managers start asking for donations to cover the costs sooner and frequently. And when people don't donate, they'll have to resort to ads. And if an instance is really popular but barely afloat, some big fish comes along and offers to buy it from them for a decent price. Classic strategy.
Meta may say it wants to start its own instance, but just wait until they see how most instances have refused to federate with them and they'll be sniffing around one of the popular instances trying to buy or offering a nice package to federate. By then, users will be established and not leave immediately.