When you think of Northrend, when you think of Arthas, and when you think of the possible "phat purple lewtz" that could drop off of Arthas's cold, icy corpse, you pretty much automagically think of Frostmourne. But is letting Frostmourne in as a droppable item a good idea? Should its dark legacy continue at the side of a player, or should it be flown away somewhere, never to be mentioned again until it strikes another NPC of the World of Warcraft?
Personally, I hope that whole "revealing Frostmourne" set of slides at Blizz-Con was a giant cosmic joke put in front of the players by a few bored developers. Giving Frostmourne, a sword with more history than some real-life players, to the hands of the player population is a deadly, deadly idea.
First of all, Frostmourne is, in all honesty, a character in itself. It would be like if someone told Tirion Fordring, the proverbial Paladin, or Thrall, the best Warchief in all existence, that he was going to be the servant of Noobio, the Tauren druid who thinks that PvP is the only useful to get honor points and phat lewt that he can show off to his eight grade friends. Frostmourne is the arm of the Lich King -- it pushed out of the Frozen Throne in Icecrown Glacier in order to spread only evil and corruption. It thinks, it moves, and it controls. For lack of a better comparison, it is Tolkien's One Ring.
At this point, we need to weigh what Frostmourne desires and what the player who wants to wield it desires. The player desires fun. They want to wield Frostmourne for the high DPS rate, the coolness factor, and the ability to completely floor their friends in PvP combat. They do not care for the story of the sword, the intelligence of the sword, or for the negative side effects of the sword. The player wants the sword to be an inanimate object that just sits on their side and does nothing else. We've already seen what happens when the player is usurped by the story -- they get angry. Very angry. The game needs to cater to them and them only. Even when all hell is breaking loose around the player, they want the option to make it go all away, even if that option cannot exist.
"Frostmourne is controlling, decisive, and restrictive."
At this point, what should they do? Should Blizzard insert the sword and put in the side effects that could, potentially, cripple a player's gameplay? Or do they put in the sword and just leave off those little "problems," belittling the sword to the point where it isn't a focal point of the lore?
Knowing Blizzard and the way they are handling lore in WotLK, they're not going to reduce Frostmourne to another meaningless item that can hang from a player's belt. So, by that logic, if Blizzard puts in the sword, it's going to carry some sort of unseen "catch" or "penalty." This will most likely lead to complaints falling about the sword because, as I stated before, players don't like penalties in this day and age.