As there is potential for abuse, it would be nice to get some clarification from SE on what will be in place to mitigate it.

Since you can't cure people fighting an NM from outside the party, for example, it may also be impossible to "assist" a party fighting an NM as well.

As far as powerleveling, there ought to be sp/xp penalties in place when someone much higher in level than you attacks the same mob you're fighting, so I don't think you'll be able to just have some rank 50 archer murder everything for a low level char for huge gains. But if that's the case, it would be nice to have some type of /blockaid lock-out if you don't want outside interference from someone trying to impede your grinding.