Perhaps if these HNMs were made as instanced BCNM fights with a time limit (like ENM fights), a lot of the grief camping them/claiming them would go away.
For Example:
Strange Portals (or whatever you'd like to call the teleporter/vortex/entrance to BCNM) would be added near all the current HNM spawning points. NPCs (like Vanessa for the Promyvion ENMs) would be added somewhere to give you the key item (Or for more challenge, a QUEST to GET the key item), and tell you when you 'can meet the HNM again.'
Example in practice:
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*Target NPCBOB, trade item*
NPCBOB: I see you've brought the item(s) I've requested, excellent. Now, which Legendary Monster shall I tell you about?
*choice box: Fafnir, Nidhogg, King Behemoth, etc*
*Select... say... King Behomoth*
NPCBOB: Ah, King Behemoth, the undisputed ruler of *blah blah flavor text* ...
NPCBOB: You'll need this KeyItem: Meteor Fragment to attract the King Behemoth.
*Obtained Key Item: Meteor Fragment*
NPCBOB: Wait.. those battle scars, you have clashed with King Behemoth recently, no? No need for words lad/lass, I can see it in your eyes.
NPCBOB: Legendary Monsters such as King Behemoth go into hiding after an epic battle to recouperate... you probably won't be able to meet him again for.... *Some Vana'Diel time*, or 10 days, 7 hours, and 43 minutes (earth time)
NPCBOB: I wish you luck in defeating this scourge, you'll certainly need it! heh-heh...
Then, when the timer's up for your HNM LS members, just make sure they have the key item, and jump in the portal to be teleported to an instanced (ala BCNM - nobody else around) area with the mob to be fought.
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I think this might work. It would eliminate bad blood among HNMLSs caused by MPK/lag attempts, camping competition frustrations, losing claim mid-battle to competition, and time zone/time available conflicts for people who can't afford to spend so much time camping. Also, if the timer to re-engage the HNMs was long enough, it wouldn't adversely affect the concept of the HNMs and their drops as being rare, at least, not the Rare/EX ones (in other words, everyone would still have to fight it a bunch across many many weeks/months to get the abjurations and items and what not, only it would be less stressful to do so).
The only problem I see with my plan, is that with instanced fights, more and more people would have access to an HNM, instead of the 1-alliance/24 hour spawn. Thus, HNM drops (the Non-Abjuration Non-Rare/EX ones) would become more common, and eventually lower-priced. Perhaps a tweak of drop rate could fix it, but... that's adding frustration back into a plan whose original intent was to REMOVE frustration...
..thoughts?