1: Make returning monsters are less aggressive. Either reduce the chance of getting aggro'ed or make it non-aggressive and non-linking to an engaged party. Basically make it so that a mob can still be intentionally engaged, but not left for someone else to deal with, whether it was accidental or intentional. This would include both monsters that defeated the party that engaged them and BST released pets.
Now this can lead to two different types of changes in the mob.
2a: Since the behavior of these monsters have changed, change what they drop/give when defeated themselves. I.e. if the mob drops an "elite" item normally, from say it's an NM, then once it changes to this "cool-down mode" it no longer drops the elite item, but some other less valuable item. Or reduce the XP gained from a cooling down mob.
2b: Change the attacks of the mob. Maybe make it so while it is cooling down it gains TP and refreshes(MP gain) faster, so it will do more damage from abilities and spells. Basically, make it so you don't want to engage a mob that is cooling down.
3a: I know it has been said that the GMs should monitor highly contested, and therefore MPK'ed, NM locations, which is generally infeasible. So instead, if an MPK is repeatedly reported near an NM pop location, have either that entire region's or just the area around the pop location logged. In other words record what happens, from the same logs we get in our chat window plus exact location and times, for about 5 min prior to the pop to about 10-15 min after the NM died. That way if an MPK is reported, the GMs have something to go by. And they also have names of all possible witnesses.
3b: An alternative to having the servers record what happens like the chat logs currently do, would be to have the individual clients keep say a 1 hour record of everything that is happening, even if the chat filters are turned on. Then make it so the GMs could retrieve this information from each of the offended/offending parties.
4: Make an non-aggro area around every zone point. But don't make it unlimited, or some static time limit. Put something in the zoning code that says when everything right at the zone has loaded, then give the player like 30-60 sec to decide what he/she wants to do. In addition, to avoid abuse, make it so while in this zone you can only move. No attacking, healing, buffing, or any other aggo'able actions, while standing in this zone until your timer goes off.
5: Move all of the highly desired items that are obtained from NMs to a BCNM type battle or quest. Make them just as difficult to obtain, but were multiple groups can obtain them at the same time. If it is an item that the developers want to limit the number floating around, then add something like the chocobo license quest, where there is a forced length of time you have to wait until you can complete the quest. Or better yet, add a high fame/level requirement to it and make it non-repeatable.
6: Setup a standard hate generating order for mobs. Then let the players know what they are, or give indicators(i.e. noticeable behavioral changes) as to what gives hate. One such order might be:
Wacking a mob.
Healing someone wacking a mob.
Debuffing a mob.
Buffing/removing harmful buffs someone wacking a mob.
Linking(if applicable).
Normal Aggro.
7: Someone posted about having a duel option. I think that for normal everyday disputes, which GMs probably don't have time to adequately deal with, players should be able to settle between themselves. Let them duke it out in a mutually agreed upon battle in front of everyone. And to make it fair, level cap it to the lower of the two's level, and make sure /blockaid is always on. And when it is over, each person it brought back to full health with no XP lose. Then to make sure it isn't abused, set it so you can only iniate a duel every week or so.
8: Do like Microsoft did with WinXP. Do a file validation test. If a player has invalid files, no updates. And with no updates, then no playing.
Now as for what these changes would fix, let me explain:
1: This would solve the standard drag and drop MPKs, as well as not remove the ability to get mobs as they are returning from a zone or where ever they might have been dragged to trying to kill a player.
2: This would make it so noone would want to steal someone else's mob. For example, if MPKs are a big deal with HNM/NMs because people want the drop bad enough that they are gonna MPK someone to get the mob, then if they aren't gonna get the drop or gonna have to deal with a pissed off mob to do so, they might think twice about trying it in the first place. Then even if they do MPK for a drop, then they just wasted their time, as well as everyone else's.
3: This would enable GMs to be able to see exactly what happened during any supposed event. Making it so that they don't have to go off of word of mouth or get conflicting stories from the opposing parties.
4: This should help with the trains to the zone, especially in areas like Crawlers Nest and Garlaige Citadel. But it would make it so you couldn't just sit in a protected area and kill mobs without worrying about stray aggro. And it would also make sure that when you zone, you have enough time to react to the current situation, but not go AFK for log periods of time while not worrying about dying.
5: This should make it so everyone has a chance of obtaining a highly desired item, but not having to save millions of gil to get it, but without taking away the challenge of obtaining the item. I love the BCNM type battles, they are a challenge and a rush to do. And if multiple people are able to do them for things like Sekrets ring, then there would be no reason or way to MPK someone for a drop.
6: If this list, or one similar, is followed then it should remove the bound mobs attacking anyone that is just passing by, without removing the difficulty of navigating a zone with dagerous mobs. And if players are made aware of what will generate the most hate, then they can make the decisions as to what they want to do near a mob.
7: Other than just being a fun way to settle disputes and lighten the load on the GM ques, this could possibly solve the #1 reason for average everyday non-drop and kill related MPKs. I know I would have loved to done this the other night when dealing with someone that just pissed me off and refused to let up on his unexcusable behavior.
8: Ok this one might not be directly MPK related, but it would stop a lot of people from using 3rd Party programs to cheat and make people want to MPK them because of it.
I know some of these ideas were probably already expressed, but this is my 2 gils worth of advice. Plus, I tried to think of ways to not alter the overall game play or difficulty, while still trying to address some of the issues surrounding what make MPK possible.