Something about giant creatures that could destroy you being there while you play really brings the scenes to life. Plus it adds that taboo factor of the places you're not suppose to go to, but you do anyways because you can't help but explore and discover.

Well if you really had to have some kind of lore behind each "world boss" you could chalk it up to Neltharion(Deathwing). He shattered the world as he entered, so why not say due to that power/energy those that didn't die were corrupted with his evil power and changed into what they are today. Sure it sounds cliche but meh.

And if these world bosses were to be implemented again what's stopping guilds from farming the piss out of them and leaving other's willing to try out in the cold? Maybe create a lockout or debuff for the people that down them for a week just like regular raids?

I haven't bothered taking down any of the world bosses at all so i wouldn't know if there's already something in place to prevent constant farming(other than a long respawn timer)

It'd be cool to have world bosses again, but exactly because guilds would farm the crap out of them I'd say the implementation should be different.

Perhaps make them lootable by everyone who "tags" them with damage before they die, and have them drop part of a quest chain to form an item. Kill every world dragon, get a sword, something like that.

phasing...

blizzard can just phase the bosses out for anyone who kills them for that week. They would also up the re spawn time so more guilds got a chance to fight them per week

Well instead of using phasing etc etc. make it more oldschool, you won't only need a 40man raid to down a world boss, you'd need 4 or even 5 40man raids to have a chance at killing a dragon/world boss. In everquest there were those kind of bosses and it was really fun to be a part of something like that. It also eliminates guilds rushing to kill the boss. What this game is missing is,besides the accessible by everyone stuff, content that isn't designed to be conquered every 7 days, it really helps to create an epic feeling and unfortunately, how ever much blizzard wants to convince us, WoW is missing the epicness of "there are big things out there that are not easily killed/attainable/whatever". Mind you i'm not a hardcore raider or a hardcore gamer but hell even a baby if you give him what he wants all the time, he has nothing to look up to..

Back on topic though,

Having 150 people might be a bit tough to handle on a system performance point of view but hey, they've made enough money out of subscriptions in the past few years so they should be able to pay someone to figure it out!