* How does your history get synced when you send a message?
* What if some of your devices are offline?
* What if you have two devices that are never online at the same time?
* What if a device is offline for a very long time? (No possibility of holding the message on a server for eventual transmission.)
* What if there's only one device currently on that receives a message and then is destroyed?
Marking a single device as the master and forcing all other clients to proxy through it removes a huge amount of complexity.