Wouldn’t it be more sustainable for
OPA to integrate Nostr?
Discussion
how would that work? we don't even have a feed
So you think Nostr is just a twitter clone? There are literally hundreds of potential use cases being built out, including something similar to OPA.
At the very least allow people to login with their npub so they can see other Nostr users and not use a private chat for npub discovery.
Relay sets based on regional location in Damus Japan now 
You could build a bridge between your paid group chat and NIP-172 communitoes with one of the python libraries like aionostr or the nostr library.