I can't develop a mod because I don't have the skills but I feel like proposing, if someone hasn't already done so, an idea.
Using the Adventurers, you could create a mod in which the travel function could be used to send ambassadors from one Court to another with the possibility of showing diplomatic proposals. Obviously, for the role of Ambassador, traits strongly linked to Diplomacy would be necessary. In this way, the diplomatic part would become deeper.