This search filter NIP can help. Only a few relays I know of support it. https://github.com/nostr-protocol/nips/blob/master/50.md

I think clients should cache/index your own events better. My whole 3,500 event history is 3.5kB. Don’t even need to search a remote server. It’s also a poor man’s backup source then.

A definitely see long term retrieval services/relays existing.