_Italic_ etc etc.
(Bonus points for emoji support)

This is for both ways.

Sorry for the very late reply! This mod aims to not modify any message sent by users. You can use a mod like StyledChat for the sort of thing. Are you okay with that instead?

I am fine with using StyledChat for messages in the Minecraft Server, however messages are currently coming in from Discord without having their discord-styling applied if it's applicable to Minecraft.
_Test message_ for example in Discord is; Text message but displays in Minecraft as; the former.

https://github.com/Gegy/markdown-chat has an API that could be used if markdown-chat is installed. this could maybe be useful

Ah, thank you for the clarification!

A part of the idea of above would be the ability to write an emoji in MC and have it correctly show in Discord. This works with default ones like :thinking: but any custom ones you have do not.

Both markdown and emojis have been implemented, closing this issue now.