For Nostr, atleast, it depends on what it wants to be. I myself don't understand what people expect from Nostr relays. I would like Nostr to be free public relays that hold events for just 2 to 3 days, unless you pay them or are an influncer that brings traffic that could be of use for the operator somehow. <- This doesn't need scaled servers. Though it looks like most of the current users and apps expect big relays and blossom servers to store events and media for free forever, which is an illusion.