You mention that nostr “works” for social clients but not yet there for “other stuff”. Just keep in mind, its at the very least debatable if it works for social:

1. No likes

2. No followers

3. Broken profiles

4. No search

5. No private messages (yet)

6. No groups (yet)

7. No stats

8. No attachments

9. Single account for life

10. … list goes on

And the answer is usually “you don’t need it and hoy you will be happy”

The thought to change query language in future is interesting.

P.S. regarding “to database or not” I personally don’t have strong opinion but rather tend to believe “relays for transmitting, layer-2 for clients”