Nip17 only works if ecash stamps proliferate. Otherwise it is trivial to spam relays into oblivion with giftwraps.

As I said before: you pay (ecash, or by self hosting) or trust (eg web of trust relay, uncle jim, group relay).

No other way I see around this.

Also it is worth putting DMs in context:
- Is it for a p2p marketplace?
- A dissident / freedom-fighter group?
- A developer community?
- A group for random cat-memes?
- One-to-one, few-to-few or many-to-many?

Don't think black and white, and don't think that one spec rules all. It almost never is the case.