It's better not to rely on a relay for this, all the filtering can just be done by a client 🤓
Why?
Mainly any client is already requesting the notes from people I follow. So it's easy to add a filter there only for displaying the GM notes. So it's basicly the same filter you're using in the GM relay 😃 Where was the NIP again to make these kind of filters portable as a Nostr event...so you could use them in a relay and/or client 👀
Kind 31890 https://njump.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 @hodlbod has this event kind a NIP/NUD proposal?
There is a NUD and a PR: https://github.com/nostr-protocol/nips/pull/1554/files