Nice idea, but how do you want to send/transmits the messages? Via the blockchain, that will be not instant and work for a very limited number of users. Or by using the conventional way that will be not decentralised.
So, what will be your invention here?
The architecture with IPFS integrated will be created to process the messages instantly & being stored through a decentralized network (p2p) . As soon as we grow we will need create and stronger network but both, instant chats + decentralized chats are totally possible.