If you simply want to know how to get it done, MMO-Champion have a simple list of steps. The Game Detectives have some more background, including the solution to the binary puzzle that proved impossible to solve in English before Chinese players figured it out using an easier set of clues.
Beyond that was a simple puzzle in Val'sharah, leading to the final challenge - the Endless Halls. This is a custom-made zone with a large set of rooms, containing orbs and runes that must be matched by colour. You can only carry one orb at once, and the layout of the maze teleports you around. It's proved a big sticking point in what is normally a simple series of instructions once it's all been worked out.
This add-on is vital to finishing it in reasonable time. With its help, I got it done in a couple of hours on Sunday morning, with liberal use of the map reset and backtracking each time I found a rune. It's still a bit of a challenge, and the RNG nature feels close to a troll after all the complaints about it in this expansion, but you shouldn't have the 8-10 hour problems the first completers did. Here's the secret Discord's image explaination of everything.
Jeremy Feasel, the designer generally associated with the puzzles though definitely not the only person with influence on them, congratulated the community and offered an explanation for one of the more infuriating red herrings. Chadd Nervig, another designer, retweeted a bunch of player's maps and explained his own problems.
As for what's next, there's likely to be another Legion patch, and Blizzard are always teasing more secrets not yet discovered from the launch of Legion or before. Of course, once the next expansion rolls around - which we're expecting to be announced at BlizzCon - there'll be a whole new set of zones to find stuff in. When that happens, expect the secret-finding Discord to see these sorts of numbers once again.
Update September 2, 2017: After defeating the evil chair, hunters of the Lucid Nightmare are now stuck in Gnomeregan.
After almost 24 hours of nothing, intrepid mount hunters discovered that you need to equip the Shadoweave Mask in order to interact with the skull atop the dingy chair. After talking to the skull, the next clue had players looking for “the shaded delegate.”
The “shaded delegate” in question was the Dark Iron Ambassador in Gnomeregan, which is where players are now stuck trying to enter a message to solve a riddle that’s written in binary. There are a row of ten consoles where players can change a number from one to nine, presumably to write out the answer to said riddle.
So far, players are stumped as to the contents of the riddle, as well as what the numbers on the consoles mean. The current theory is that the numbers correspond to words in the alphabet, and that players have to spell out a particular word or phrase.
If you want to keep track of the current clue and the prevailing community theories, check out this continually updated Google doc.
Update September 1, 2017: The search for WoW's Lucid Nightmare continues, with a chair-based roadblock the latest challenge.
Things moved quickly after our post earlier in the week, with World of Warcraft's latest big puzzle looking like an easy one for a few hours. Busting through a few early challenges, the combined might of the community has come to a screeching halt in front of a hidden chair.
You can read the full progress to this point in this Imgur album or handy Wowhead comment. Both will be regularly updated. Quick version: scroll in Dalaran lead to Ulduar, Ulduar had a lever that gave a light puzzle which lead to Ahn'Qiraj, where people played Bejewled until they were pointed to Deepholm. There was a chair there.
On the chair was a distorted message reading "Supremacy? Get… Shirk… …eke..." After 24 hours, that's still where they're stuck. As you can see in this Google doc, quite a lot of stuff has been tried, suggesting brute forcing the problem isn't going to work. After some early successes, this is looking just as tough as the Mind-Worm.
It sadly hasn't been a completely innocent search. While the spirit of co-operation is strong, the individual who first worked out the Ulduar puzzle posted to Reddit explaining how they were pulling out of more puzzle solving after the reaction he received. Death threats for perceived internet slights are bad enough, but this guy was just trying to help people.
For now, the Discord channel continues to grow at speed and doesn't look likely to slow down any time soon. There are 10,953 online at time of writing, and far too many to count in the voice channel - easily in the high hundreds. Blizzard watch on semi-silently:
<blockquote class="twitter-tweet tw-align-center" data-lang="en"><p lang="en" dir="ltr">Sorry <a href="https://twitter.com/discordapp">@discordapp</a> server engineers, at least we're providing you with useful data? :) <a href="https://t.co/zPMb9sQM7a">pic.twitter.com/zPMb9sQM7a</a></p>— Jeremy Feasel (@Muffinus) <a href="https://twitter.com/Muffinus/status/903384088475688960">August 31, 2017</a></blockquote>
Original story August 30, 2017: While fighting in Legion PvP may increase your character's Prestige level, WoW players know that actual prestige comes from having the newest, hardest-to-acquire mount. And so the announcement of a new hidden mount in the latest patch (7.3) is certainly of interest. According to the Wowhead listing, the new Lucid Nightmare mount will drop from the aptly named "Puzzler's Desire."
Senior game designer Jeremy Feasel - @Muffinus on Twitter - is staying mum. "We will never provide any hints. Nothing we say or have said will be a hint. You do not need to follow us on Twitter to play the game." What you may need to do if you want to be among the first to find the secret mount, however, is to link up with the WoW Secret Finding Discord Group, who are already gathering plenty of clues.
The first clue found so far is an Inconspicuous Note which shows a smoke-fogged purple brain surrounded by chains. A Rusty Lever in Ulduar also seems to activate a large light grid, once the player has read the aforementioned Inconspicuous Note. More notes are being gathered in the Puzzler's Desire Google Doc, for those who want to follow along.