Earlier quoted context omitted.
There's already p2p messaging apps that do that without any blockchain nonsense. The blockchain would leave a permanent trace to which pseudonym posted what forever.
P2P messaging apps have a hard time with group messages because you have to have someone online to relay messages at all times. Group chats really have to have a shared storage medium to work.
I can see the value in the distributed part certainly but if the storage requirements are very large due to a large volume of messages (I'd imagine any solution which caught on could quickly outpace the number of transactions on something like the ethereum or btc network), wouldn't it necessarily just end up centralized?
It's an interesting idea though.