Title: Low level marriage diplomacy.
Summary: Allow individual characters to get married. Married characters would automatically be neutral observers for any battles with their spouses realm. Marriages have been an RP thing in the past, but if we include a mechanics aspect of it with consequences that can't be avoided, it could be used much more effectively. This would be for as long as the characters live, no divorce. Marriage would not be an IR for characters. Rulers could forbid marriages, and if the character follows through with it, they will have the wrath of the ruler on them.
Details: An option would be added where if two characters were in the same region, they would have an option to propose marriage to another character. I see this mechanically happening similar to trading a unique item. One party proposes, the other receives a message where they can accept. If one character leaves the region before complete, it will be canceled. A warning message would have to be included stating that it is permanent and that they will not be able to take up arms against their spouses realm. Characters would have a line added to their Character Page below the line stating their position, like "Married to Sir XXX of Realm X on DATE".
Benefits:
1) Increase RP availability. There is RP of the wedding, but also if a spouse is killed or wounded, it would involve drastic vengeance plots. Also allows for "Romeo and Juliet" scenarios.
2) Diplomacy. All through history royals were married to other royals as peace deals or alliance builders. The same would be done here. It would require commitment from rulers, and could get delightfully awkward if relations between realms fell.
3) Lower level politics could be utilized. Marriages could support not going to war, or an assault on a loved one could push a realm to join in on a war, giving more cause than "hey we are at peace let's get in on this".
Possible Downsides or Exploits: I can see this being done arbitrarily and regretted, especially when it is first introduced and the novelty is high. However, I think that will pass quickly, especially if there is a warning message that it is irreversible.