Suggestion:
I've looked for other plugins that would do this, it's self explanatory, each world has their own chat, and you can't see the entire server chat. I've seen a plugin that does this but it isn't maintained and I think it would be a great addition to MV core.

So I've tried the unmaintained plugin: https://www.spigotmc.org/resources/perworldchat.29897/ . It half works, so you can list the chats that should have a single chat, but doesn't work when it comes to connected worlds (a world with and end and nether). If you're going to use their source code, take this into consideration

There are many chat plugins out there that has this feature, ranging from plugins like Chat Control, Chat Manager, DeluxeChat, VentureChat and probably more. So there isn't much of a use for mv to create a chat plugin.