Very interesting. Are any other clients doing this? Would you envision clients sharing filters like this?

I don't think so. Everybody just saves a huge list of relays in their databases. There are many places clients could share bloom filters. This all started with this idea:

GitHub

Per-event AUTH keys by vitorpamplona · Pull Request #1497 · nostr-protocol/nips

This adds two special tags to authorize certain keys to download events. This is similar to NIP-70, but in the opposing direction (read instead of ...

In this case, I proposed sha256 as a hash function so that clients didn't need to code MurMur3, but MurMur is so easy that we can just teach people how to do it.

for this size of a set, the WOA scores, about 100k scores. so it's very doable to just grab the scores, either with http api or websocket attestations..