JoinMarket is already decentralized, there is no central coordinator and no single messaging channel. Although improvements are possible there too (for example, message channels are list in config file, could use some gossip protocol to find new directory nodes). https://github.com/JoinMarket-Org/joinmarket-clientserver

Another decentralized idea is DMix proposal by Fedi Barbara. https://fadibarbara.it/papers/dmix.pdf