I'm not entirely convinced this needs a blockchain. I guess Hyperledger (Fabric, I'm assuming) is a handy way of guaranteeing a total order for a channel's messages / events and making sure history is immutable, but it seems a bit unwieldy for a distributed messaging app despite being somewhat modular.

Most of their goals aren't specifically dependent on anything blockchain-like, and the ones that are seem like they could be implemented in a much "cleaner" way than having to bring in Hyperledger and all that it involves