One could imagine it being a kind of emergent community-organized event, somewhat modeling a decentralized peer-to-peer network itself. There will still technically be at least one intermediary of a sort, but hypothetically the only real intermediary could be restricted to the single person or group who initially proposes the event and issues the batch of ticket NFTs.

There are plenty of major concerns here, like how security and access are physically enforced if there are no official organizers or designated volunteers, but in theory you could maybe distribute a phone app so everyone is automatically scanning for unauthorized people, and just rely on physically capable attendees and police to deal with potential security incidents. Still probably a recipe for utter Fyre Festival-esque disaster and lawsuits in many cases, but feasible in theory.