Riddle Me This: Decrypting the Lucid Nightmare

The Mind-Seekers seem to have a penchant for leaving their notes in obvious places. Maybe they want us to find their treasures? Maybe they feed on our thoughts? That’s probably not important…
What was important was an Inconspicuous Note, sitting on a table in the Curiosities & Moore shop in Dalaran (Broken Isles):
It begins in the 2104059.
With a most pleasing sign.
(These letters will not always rhyme.)
2104059, of course, is an anagram of 2009-04-15, the date of the Ulduar patch notes on the official World of Warcraft site. From there, players combed Ulduar for clues. Observant players discovered a new lever in the XT-002’s room that they could interact with among the piles of scrap. Pulling this lever summons a massive 20x20 grid of Scrapyard Lights on the floor of the room. Interacting with these lights toggles them on and off.
In the Inconspicuous Note, the Mind-Seekers requested a “most pleasing sign.” Many signs and symbols appear in Ulduar, the most prominent being the four symbols of the keepers of Ulduar. Of the four symbols, the most pleasing to the Mind-Seekers is evidently that of Mimiron: a gear. Players needed to draw this symbol of ingenuity with the lights in order to progress.

The way is now open.
To the greatest secret never told.
A fitting end to your journey.
The clue here is a reference to a place in the world that has long been a secret to those in the know, but has never been used—the horrendously creepy Forgotten Crypts in Karazhan. In the game since the WoW’s initial launch, exploration-focused players ventured into these crypts for years after each patch, in the hopes of finding some newly-added secret. They were perpetually disappointed—until now. 
This time, sitting on top of a pile of bones near the bottom of this huge-but-empty crypt (within The Pit of Criminals) is a chest containing the [Lucid Nightmare].