One thing to consider is that even if people actually start quitting over multiboxing, I doubt that would do much. Either the people who threaten to quit about other issues are serious and go through with it or they're just faking it. But in either case, pretty much every one of those issues (imagined or real) still exists in the game (i.e. "X" class is overpowered as well as other dumb things). Unless there were a massive exodus all at once, I doubt anyone would notice or even care.