I think wow got in trouble because players felt grieft by multiboxers. In diablo 3 there is no pvp and you're not taking loot from other players or anything... perhaps that is why we're still safe?. I think it will depend how pvp in D4 works and how unfair the advantage of multiboxers is perceived by the regular players... depending on that it will be tolerated or not.

I hope they design the game so that multiboxers can just have their fun with it... without ruining other peoples fun. As long as their no complains we can go are merry multiboxing way.