They pulled the link down already, but I still had it open… so
https://i.gyazo.com/a9d72a571afbe2e862ee20f0eb13324b.png
As a note the 403 error you get on the actual link for the layman means they locked the page’s access permissions so outsiders cannot see it. The page still exists.
What did I say about thread titles >: (
It mentions it on page 171 that he tried to destroy him, the book ending, and that later the spirit of Ner’zhul recovered. They go to war in his mind and, as you said, he was left as “a wail of sorrow in the back of the Lich King’s consciousness. Arthas found it easy to ignore.”
Easy for Ner’zhul to recover since Arthas did the same thing to him as he did to his Human Soul: stab him with Frostmourne which in the Human Soul’s case fed the Soul to Frostmourne which of course means that Ner’zhul was fed to the Blade.
Since Ner’zhul is the one who enchanted Frostmourne to steal Souls after the Nathrezim made it he naturally escaped with ease, started a fight with Arthas inside his mind and made statements to the Players in Howling Fjord about once being a Shaman before being reduced to a wail of sorrow by Arthas who played on his guilt.
Frostmourne’s only known purpose prior to Ner’zhul modifying it seems to be freezing things. Frostmourne was the Dreadlords’ Ice Sword while Apocalypse was their Plague Sword. Ner’zhul improved the weapon after getting it.
Source? 
No, it gained that property at the time of its creation. It is a Nathrezim artifact like the helm of dominion.
Tichondrius mentions it in the Arthas novel… While retconning the Warcraft 3 statement of Frostmourne being created by the Lich King in favor of having the Nathrezim create it.
No.
https://wow.gamepedia.com/Frostmourne#Origin
When Ner’zhul was transformed into the Lich King by Kil’jaeden, his disembodied spirit was shackled to a magical suit of armor, as well as the runeblade Frostmourne, and trapped within an icy tomb called the Frozen Throne. Both the armor and the blade were crafted by the nathrezim[4] of the Burning Legion[5] for the purpose of containing and controlling the Lich King. When they crafted the Frostmourne, they had shielded themselves from its power so that their souls wouldn’t be consumed by the blade upon being defeated, but instead, they would return to the Twisting Nether,[6] as the souls of demons normally do.
^ World of Warcraft: Chronicle Volume 3, pg. 53
So Chronicle Retconned the Arthas Novel just as said Arthas Novel retconned Warcraft 3!
https://wow.gamepedia.com/Retcon_speculation#Frostmourne
Frostmourne
In Warcraft III: Reign of Chaos,[18] Tichondrius claimed that the Lich King forged the sword. However, Arthas: Rise of the Lich King revealed that the Nathrezim forged it,[19] thus invalidating Tichondrius’ first statement because, if his race created the sword, it would be odd that their leader knew a different origin.
^ Arthas: Rise of the Lich King, pg. 204
I don’t think he’s going to be a villain, I think we’re looking at a case of Vader Syndrome here, honestly. The blue is probably meant to signify him calling on his powers to actually command the Scourge. Hell, his body is still fiery, so we’ll probably get a line like “My mind may be the ice of death, but my heart is still dragonfire.” or something equally dramatic.
Colour me shook, I am actually surprised this one seems to be legit. I guess in the end all of those ‘proofs’ were just over reactions on our part?
Certainly will make those who use photoshop lines as ‘proof’ of fake be less creditable.
I’d argue that was first retconned in the Frozen Throne, where it was revealed that Frostmourne was originally part of the Frozen Throne that Ner’zhul casted off so Arthas could find it.
Honestly, I don’t see Tichondrius claiming that frostmoune was made by the Lich King as something that was later retconned. I see it as Tichondrius lying to Arthas, as Tichondrius was still playing the “servant of the Lich King” role like Mal’ganis did in order to gain Arthas’ trust (Arthas was going to kill him). Hence why Kel’thuzad tells Arthas later on not to trust the dreadlords, as they are Ner’zhuls jailers, not his servants.
but i1m not talking about him, i’m talking of the only leader capable of taking care of the undead, the only one who saw the truth in the lies of the jed…horde!
I’m a loyal follower of the chosen one! Sylvanas Windrunner!
I’ll finally join her in taking care of this usurper and the scourge will finally be free of the tiranny of the helm of damnation!
I believe it would not be amiss to warn you to perhaps manage your expectations a liiiiiiiittle bit. Just a tad. 
Well, apparently the Bolvar thing is tied to some art list. Assuming it’s legit, it shows some characters for next expansion I guess;
Bolvar, Vol’jin, Galakrond, Mueh’zala, Thrall, Anduin and Sylvanas.
Well I was already interested and now I’m really interested.
But that’s mostly because I think Bolvar’s Sindragosa being Galakrond would be kind of epic in a horrific kind of way. Unless Sylvanas gets there first.
I’m kinda figuring, if it’s legit, he’s related to the dragon side of things, not the undead. Like, we see it in the Shadowlands, or some manifestation on the Dragon Isles, or something.
World of Warcraft: Compassion of the Lich King
Could be both. Maybe we need the aspects to help fight him so we help them try and get their powers back. Could be the excuse to get a new black aspect and have Murazond finally happen.
Or you’re right, but either way it’ll be interesting to see what they do with him if true.