This will never become a rule for a few reasons;
-It will be extremely difficult to regulate and enforce
-There will be an outcry of players who are against the decision to make it bannable
-Staff will have to ban hundreds of players who are either not aware of the rule or who disagree with it
-It's so easily countered by finding your own team mate to go into combat with you
If you're having that much trouble dealing with teamers, I suggest slowing down your pacing a little bit. Find a nice smooth bow, some razor sharp arrows and camp. If they complain that you're being a coward, just explain that it's your way of dealing with players who team; both are legitimate battle strategies. They'll get impatient at some point and make a wrong move, and you can hit one of them off. From there, it's a fair fight :)