If you take a look at a blue post announcing the changes to their policies with regard to multiboxing:
You will see that it says “as activities which effectively replicate automated gameplay are contrary to the terms and conditions of the Blizzard End-User License Agreement (EULA).” So yes, they announce in an official posting that a decision has been made that a certain action now contravenes a ruling in their EULA. It actually says at one point:
“Prohibited Commercial Uses:…performing in-game services including, without limitation, account boosting or power-leveling, in exchange for payment;”
The words “including without limitation” means that they can define what that means and how far it goes. So really would they even have to change the EULA - all they would need to do is say that payment for carries was banned under the EULA.
I don’t know that they ever will, but then I didn’t think they would ban the use of input broadcasting software, which effectively smashed much of the multibox farming that has been in the game for a very long time.