The questline is only available to cloth casters (but could be extended to include Druids & Shamans, or perhaps be limited to Mages only). Upon defeating Malygos in the Eye of Eternity 25 the Heart of Magic object is spawned to be looted, but instead of being the objective of the existing quest, this questline requires it to instead drop either the intact HoM, or the cracked HoM, which both start a quest. The intact one is available to all non-cloth classes and would follow the questline that exists in the game already, where you just hand it in to Krasus and get a necklace, but the cracked HoM, whose quest can only be initiated as the correct class, will initiate the legendary questline. The task itself is simple, as it requires you to simply go through the HC Nexus & HC Oculus and use the Attuned Crystal near the respective Ley Line streams (can potentially be extended to Eye of Eternity too). Posessing the Attuned Crystal could cause stronger Arcane Elemental mobs to spawn inside the dungeons, who would either fight the remaining Blue Dragonflight enemies (who still believe in Malygos' ideal, even though he already perished), or just replace them from the get-go, similar to the special encounter of Quel'Delar inside the Halls of Reflection.
This is not a quest about difficulty, but a quest about persistence. As it says in the story, it could take weeks, perhaps even months of clearing the two (or three) dungeons every day, fixing things bit by bit. Maybe it would require you something like 60 times to use, maybe more, maybe less. If the Arcane essence is gathered as an item, then the values could also be drastically randomized between 1-10 out of 300, or something like that.
And when you do persist, and fix Malygos' mistakes, the Wyrmrest Accord will reward you accordingly.
It is to be noted that the Heart of Magic is not Malygos' actual heart, but they way it behaves could be more than just metaphors. Whether the spirit of Malygos actually accepts you or not, nobody can be certain.
Now the Staff's stats base on the Heart of Magic. The core mechanic, is that your Character would need to be mentally strong enough to effectively use it. Intelligence is supposed to be taken literally. If your Character's mind is too weak, as in low Intelligence, the Staff gives less Spellpower than it should for its itemlevel. Conversely though, if your Character has an incredibly high focus on intelligence, they will benefit greatly from the Staff (perhaps even too much, I have not crunched the numbers for a min-max build). The sockets further support this idea with additional scaling intellect and yellow Sockets instead of red (for yellow or orange int gems).
Ironically, the item's lore and stats fit perfectly for who would use it lore-wise: an arcane mage.
Since the arcane spec bases a lot around mana, or rather is quite mana hungry, having high intellect will not only increase damage, but also sustain that damage by increasing the mana pool, thus also increasing the efficiency of % mana regeneration such as Refreshment and Evocation. Arguably, the only con would be that a focus on Int gems would replace the focus on Haste gems which is vital for Arcane Mages.
The crit gained from an intellect heavy build is what makes it viable for other classes too, so it doesn't just become a "Gnome Arcane mage BiS item".
It's worth noting that I've not considered it for use within PvP, as such I don't know how balanced it would be considering Mana-Burn. In the end, I don't even know how balanced it is for a true min-maxed PvE build.
And while the Heart of Magic is supposed to be an actual overpowered item, the mind of a mortal, however adept they may be, can only harness a fraction of its true strength.