Support for the Discord Rich Presence API should be implemented, such that a user can see the status of another user's OpenTTD game.
Some potential things to display in RP:
Single/multi-player (+ server name)
Additionally, supporting the join capability would be a value-add. This may require some discussion, as there's two ways to implement this - either a join button in the Discord client, or an "ask to join" button on the client, which pops an in-game message to invite the other user to the server. With password-protected servers/companies, we should consider exactly where the join functionality should take them - there's no way to have both a join and a ask-to-join button at the same time. My current thoughts would be to have a join button for servers without a password, and an ask-to-join button for those that do.
Thank you for your suggestion. Currently we have no plans of adding this functionality (neither for other platforms like Steam, Twitch, etc). But we always welcome contribution, and if you feel up to it, we are more than willing to look at any Pull Request that might enable this.
One important point that isn't solved with code is that to implement the Discord API in the game, OpenTTD needs to be registered as an organization with Discord to get API keys, and someone within the project needs to be owner(s) in that org. Without that it isn't becoming an official feature either.