To be more decentralized you could use radio waves outside of the Internet like LoRa to broadcast whatever you need to... maybe it could be combined with the Internet if it's available to increase distance.
Not having any LoRa hardware, I've been imaging just using Bluetooth to gossip updates with people in the same elevator, at the same stoplight... I'd love to build something useful that could tolerate a transport layer like that
One thing that pisses me off is that Google never implemented WiFi "Ad hoc" networking on Android (reducing the probably of decentralized networks taking off).
But I would also love to see something like this going.
When I work on that project I often consider it as a weapon against the Googles of the world, so it's not surprising that they haven't made things easy. If we want to cut them out of the loop we're going to have to rebuild some of that loop.