Just to argue this point, this is actually already solved. By doing so, they'd be breaking other game rules. Now, whether Blizzard enforces them enough for players to take it seriously would be a point to consider, but technically rules against that kind of trolling do exist.
I'm okay with punishing innocents here, because I don't think it would ultimately punish too many. Yeah, it sucks if you have to legitimately leave a group for non-nefarious reasons and you end up with a debuff or whatever the case may be, but for every one person that gets a penalty for the wrong reason, at least a dozen will get it for the right reason. And the number of people who incorrectly get penalized will go down as people get better at planning for instance participation. I do think they'd still need to add a few additional tools - maybe give group leaders a "remove without penalty" command to help even it out.
I doubt Blizzard will do anything at all, though. I still remember when they added rules in Wrath that severely punished toxic players - only to quietly roll them back when they realized getting rid of bad people hurts their bottom line more than just letting them shit up the game.