A great, welcome change, multiboxing was always ruining Wintergrasp.
The mboxers are "having fun" at the expense of other players. Besides, considering that external input-macroing programs are a requisite to multibox, I fail to see how multiboxing supposedly isn't cheating. Nobody is clicking those game windows separately and manually inputing keys into each game window, they're using a cheat program that will automatically macro inputs to the other characters' game clients.
Making it less likely to encounter multiboxers in WG is a step in the right direction, but obviously multiboxing should have been entirely banned from the beginning, or at the very least banned from participating in PvP.
Or make a blackrock-style PvP realm for multiboxers where they can play against each other. Then they wouldn't be "having fun" with their cheating against other players, but playing against other multiboxers. See how much "fun" they're then having when they can't just nuke solo players with 5 macroed spells that happen in the same instant, but have all other players with similar setup against them, making the playing field even.
Because let's face it, no matter what mboxers claim, they aren't doing it to compete fairly against other multiboxers but to unfairly nuke solo players with an unfair advantage of having multiple characters and macroed spells they can cast multiples of at once. I guarantee that a blackrock-style PvP realm for multiboxers would be met with whining and resistance from the multiboxers because they don't want to play fair.