Marrying digital with physical is an interesting approach. The problem of proximity is a unique point of friction which might also temper digital communication.
If the application "lived" on cellphones and communicated with a P2P protocol, users could truly own their data (excluding the data they share with their network).
I imagine that some subset of users (1/10th?) would need to aggregate and serve their own and first-tier friends' content from a cheap VPS, and the Kardashians and Elons of the world might need a CDN of some kind, but if it's limited to short text posts I imagine it would be a tractable problem.
Marrying digital with physical is an interesting approach. The problem of proximity is a unique point of friction which might also temper digital communication.
If the application "lived" on cellphones and communicated with a P2P protocol, users could truly own their data (excluding the data they share with their network).