If drops only end up with those with the open quest, then the higher level players will have no reason to kill steal. However, this may prevent the higher levels from being willing to help those who need the drops, as they will waste idols etc. for nothing.
It's a sensitive situation and I think some long, hard decisions need to be made about this, that most people can agree on. To me, a target lock doesn't seem very popular and so it may not work.
I would suggest calculating the drops depending on the group: a group of 1 will only gain 1 drop and a group of 7 will gain 7. That way, a group of one will have a smaller probability of getting a good drop than a group of 7. On thy situation, all users will feel that their hard work fighting a boss will be paid off. If a user does kill steal them, then they will not get 7 drops.
If you were feeling especially harsh, you can use a similar algorithm to locking the target but instead of locking it, if a person is registered to get the kill even though the lock is not in the favour, then they will lose the amount of gold equal to the health of that boss. So if someone kill steals a boss of 10000 health then they will lose 10k. Alternatively, a user that gets the kill against the lock will not gain a drop, neither will the other group.
Another alternative could be indirectly solving the issue. For example, putting limits on bosses whether this is a upper level limit, combined level limit or another limit. Another way is to alter the basis of the game. This may be a huge compromise but changing the way the economy functions could help to prevent people becoming so greedy in the first place. Or a system which could encourage higher levels to WANT to help lower levels complete their quests and get drops.
As said earlier, it must be reiterated that no decision of this sort should be taken lightly as it can alter the mechanics of the game in the long-term.
Thanks!
