Loremaster of Draenor

This is one of the achievements for the upcoming 'Draenor Pathfinder' meta, required to unlock flying in Draenor!

To fully complete the Draenor Pathfinder meta-achievement, you will need to complete: Draenor Explorer, Master Treasure Hunter, Loremaster of Draenor (A) or Loremaster of Draenor (H), and either Securing Draenor (A) or Securing Draenor (H). You will also need to attain revered reputation with [faction=1849], [faction=1850] and either [faction=1847] (A) or [faction=1848] (H) depending on your character's faction for Tanaan Diplomat (A) or Tanaan Diplomat (H).

There is also mention of a rylak mount, [item=128706] as an additional reward. The ability to fly will apply to all of your 90+ characters after any one of them possesses all the prerequisites (So, no need to grind reputation on every alt that needs to fly), however it will not appear in 6.2.0 but rather in a later minor patch (referred to as 6.2.x). Note that Draenor Pathfinder is account-wide, it has been confirmed that you won't have to 'earn' all of the achievements on the same character but merely possess them on said character.

Quote from the Dev Watercooler on Flying:

In an upcoming Public Test Realm build, we will be introducing a new meta-achievement called Draenor Pathfinder. You’ll earn this achievement in Patch 6.2 by mastering the outdoor environment of Draenor—exploring Draenor’s zones, collecting 100 treasures in Draenor, completing the Draenor Loremaster and Securing Draenor achievements, and raising the three new Tanaan Jungle reputations to Revered. Initially, this achievement will award a rylak mount: the Soaring Skyterror, one of the native beasts that roam Draenor’s skies. Players will remain ground-bound on Draenor until a small follow-up patch (6.2.x), when all players who have earned Draenor Pathfinder on at least one character will unlock the ability to fly in Draenor on all their level 90+ characters.

Is this an account wide achievement?

I would highly doubt it since you have earned the achievement. I didn't lose my explorer achieve when MoP or WoD came out, and it would work the same way.