There is a lot of misconception around how multiboxing works on here which is sad as it’s making a lot of people mad for wrong reasons. Also though, I might be ignorant on what is really making people mad so there is that.
If it’s the grief someone is causing by “instacasting spells” from a large group of toons at once, yes, this will help stop that. If that was the real problem than it’s awesome that this will help as frankly that would be annoying as heck if it was happening.
If it’s grief caused by mass gathering of nodes, mass killing of mobs, or just a lot of toons milling around on top of each other, this has almost zero impact. You can still use software that will open up windows between your various wow clients. Basically creating a window on one client to the screen of another client (to click through to toolbar). Mass gatherers have no interest in the game visuals so they will just fire up x number of clients align x number of viewers to the clients within their screen, set up macros on each client and then continue farming like mad. All of this set up can be scripted and recreated easily so the actual effort involved in setting up and also resetting up if banned is quite minimal. I really don’t see any issues with staying within the terms of service as currently stated and doing this. Every client will still be driven by one click in one client and no broadcasting. Efficiency will be impacted but given I would imagine a huge chunk of these are being done by gold farmers it will be no real consequence to them as the labor is cheap.
I do feel Blizz’s pain here as they are trying to solve a problem which like many things will have huge impact on a small number of people that weren’t the problem in the first place and the ones they are trying to impact will find the work arounds. Though I am one of those few impacted negatively who wasn’t the problem, I do commend them for at least trying as from the posts on here it really was obviously negatively impacting a lot of players game satisfaction so something had to be done. Tough spot to be in.
I might be wrong but will be curious to see.