So if I understand it correctly, this could be packed into the following scenario:
1) By default program the units with a default mac, a default ID and uradmonitor.com as single server
2) When the unit connects, it would download a freshly allocated mac/device ID and a list of alternative servers and store the data in its EEPROM.
3) Periodically, the unit would check if other alternative servers are available (and delete those that are offline).

Would this work? Does it cover everything, enough to make this decentralisation stand?

I believe the logic will require only a minimal code, that can fit in the available flash memory. The only issue is I find multiple transmissions of the same data to multiple servers a bit redundant (not a big issue though).