I don't see how such a mechanic could be exploited or abused.
You can't figure out, therefore it's impossible?
Off the top of my head, I can see at least three different ways that this proposed mechanic could be used to abuse the message system or prevent players from participating in the game. And at least two of them have already been done before in one fashion or another. It has resulted in certain game mechanics being altered to prevent such behavior in th future. And no, I'm not going to publicly detail ways to potentially abuse game mechanics. Battlemaster players are clever enough at finding ways to abuse mechanics without any help.
Ongoing conversations between a specific group are not even prevented in the first place given the existence of message groups.
Which have limits associated with them.
But let's say for example you have two characters in a realm that have a problem with each other and it's becoming disruptive.
Have the ruler create a message group for you. You've already got him involved anyway. Or hold it in public, and let the rest of the realm get involved. You may consider it disruptive, while other may consider it interesting, or even fun.
