We have data on what it costs to run a sizeable instance of Lemmy and it’s not a lot. How does Piefed compare? Anyone starting an instance who envisions it growing large has to contend with this question.
I don't think this is a major concern yet. The largest PieFed instance has 308 active users, 2nd place has 34. They've got room to grow.
https://piefed.fediverse.observer/list
People can start posting about PieFed on Reddit and see how the Reddit users react.
I think it's unlikely that they would attract such a large number of users with 1 post on r/RedditAlternatives or something. Lemmy gets spammed everywhere and we usually don't even gain 1000 users a day overall across all instances.
There's already been some comments about PieFed and they didn't result in huge surges.