Pointless. Anything "agreed" is possible to work around with alts (as usual). Adding stupid restrictions on social interactions wouldn't benefit the game.
Having some sort of ingame representation of a treaty is cool, but we have parchments for this. And full freedom of what to do with them (respect it as the only holy thing to you or wipe your arse with it, speaking of which, that's actually really needed change - a new emote). Unlike any built-in mechanics.