Downsides might be congestion and i think @fiatjaf would likely have a "fit to purpose" argument, where using nostr for this and ( possibly expanding the protocol parameters in the future if this gets popular) overextends the censorship routing and message delivery focus of the relay structure (the way the lightning project and its advocates did to Bitcoin) But i don't want to speak for fiatjaf. It's great to innovate but it's also great to be vigilant that certain things are building their own path to eventually forking.
🤔 I see your thought process, but ecash is just data and especially if it is encrypted data, I don't see how you could fork really, there are unofficial event types that aren't officially documented, is that a fork? Relays that support features that others don't, but unlike Bitcoin, there's no consensus thing to say "I only talk to people who do X and don't do Y" Also, with regards to being any sort of transmitter of anything, the mint should be the first target. Otherwise everything is a transmitter including whatsapp.