mostly the issue is the dumbasses who are moaning about how they think authing is like being strip searched aren't being creative about this at all
there is temporary and one-time auth and rate limiting
tor/vpn is esssential if you actually want to decorrelate your identity
there is micro-accounts with keysend/AMP prepaid balances for short term use, which could extend to one and mult-level indirection of message relaying (i wrote a whole protocol for that which is capable of handling a high bandwidth network)
blinded signatures and zero knowledge proofs could be used in several different ways to dissociate payment and redemption
mostly the issue is client side anyhow, and it's mostly client devs who are complaining about relays needing to auth to stop spam