What would the storage requirements be for a blockchain like that? It seems to me extravagant... and also would there be all the concensus algorithms? So I'd send a message and wait X amount of time for the network to achieve concensus that I had posted the message?

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.