The quests seem to involve multiple tiers of raiding, meaning that you won't be able to get a legendary at the end of the first Mists of Pandaria raids and will have to be in it for the long haul to acquire one. This avoids the problem of early legendaries (such as Dragonwrath or Val'anyr) being adjusted in later patches. However, the very possibility that this will be a legendary that anyone can get means we need to consider the effect it's going to have on your raiding group.
Josh Myers wrote up a post earlier this year detailing all the problems legendaries can cause. Now, imagine a legendary that you have to work out the process not based on class or role, because anyone can get it.
Do you give it to the tanks or healers first? Do you get it to your best DPSers so you can increase your raid's output? Do you give it to the players with the best attendance because you know they're going to be around?
And since this is a multi-stage legendary that may take the entire expansion to finish, it's possible that whoever starts the chain first might stop showing up before it finishes. Take every issue raids had with Dragonwrath or Val'anyr (legendaries that could be used by all caster DPSers and all healers, respectively) and multiply them by the Fangs of the Father quest line (which requires a significant time investment), and then extend that to include all ranged DPSers (even hunters) and all tanks as well (some tanks haven't had a legendary yet, period; I'm looking at druid tanks here) -- and then imagine the contention this could cause in your raid group.
It also means that you're going to have to figure this out.
The divide gets bigger
It's also going to affect 10- vs. 25-man raiding. This is an already heated topic, with each side of the debate convinced it's getting the raw end of the stick. Now, with the quest line for this omni-legendary involving killing various raid bosses, collecting drops and then waiting for patch 5.1 to continue the quests, you're going to see a lot of logistics.
Can two players be on the same leg of the quest at the same time, or do you have to space it out and finish one's collection before another can start it? If a legendary-collecting player isn't there for a night, can someone else get those sigils? Do enough drop in both sizes of raiding to get someone ready for the next stage in any reasonable time frame? Are we going to end up with six or seven people waiting for patch 5.1 and then have to decide which one of them gets to start the next leg first? Will 10s be way behind 25s and feel forced to play catch-up?
Class and Encounter Balance: A whole new fulcrum
This doesn't even lead to issues of class balance. Fights will have to be designed with the idea that someone's going to get that legendary. If they're designed too leniently, the legendary will feel ludicrously overpowered. If they're designed too strictly, the legendary may come to be seen as required for specific fights.
If the tanking shield legendary (assuming there is one) is designed so that it has an awesome proc or on-use that mitigates the extremely potent ability of the last boss of an expansion tier, then your guild may be punished for giving the legendary to your casters first, even if there's no way you could have known it would happen. Will you be forced to go back to the previous tiers to farm up sigils for your tanks?
However, for all my cautionary ways, I have to admit I like this idea and want to see how it plays out. The idea of a legendary that you start building at the beginning of the expansion but which only comes to fruition later intrigues me, since it's a way of keeping the item relevant. And at least anyone can get to see the lore of this quest line; it's not class-locked or role-locked. It's certainly an improvement over random drop legendaries like the Warglaives of Azzinoth or Thor'idal.
Mostly, we'll have to wait and see and be aware of the pitfalls. Orange pixels are awesome, but they're not worth destroying your raid group over.
It's open warfare between Alliance and Horde in Mists of Pandaria, World of Warcraft's next expansion. Jump into five new levels with new talents and class mechanics, try the new monk class, and create a pandaren character to ally with either Horde or Alliance. Look for expansion basics in our Mists FAQ, or dig into our spring press event coverage for more details!