Even if this exploit was fixed today, there would still be people leveling by having a level 70 friend kill mobs after they tag them, effectively wiping areas in the same manner. With the current method being so widespread now, it's only a matter of time before everyone who wants to do it will have done so and zones will be back to relative normalcy. Taking into account that they say they're patch this in 5.0 means it's a one time annoyance for those leveling the old fashioned way.

Overall, this is a side effect of leveling being inherently unfun for the vast majority of players, but a necessary evil to keep people subbed. People are going to find the efficient route to get past leveling yet another class by using 1 button rotations to whack enemies in zones we've explored and become overly familiar with over the span of half a decade.