My theory is that Xe’ra’s body looks awfully similar to a Coffin…
Illidan exploded Xe’ra so we weren’t able to see what was inside and yet:
“Its surface blazes bright, masking shadows below.” - Il’gynoth
Furthermore we hear another piece of info from Il’gynoth:
“The blind queen wields a scepter of bone. From the deep, she calls forth doom.”
According to Tauren Myth the Earthmother inserted Mu’sha into one of her Eyes.
What if it was infact a Night Warrior she inserted into her? This brings us to this line from N’Zoth:
“She is not the last, but the first. Drown her and you will see.”
Xal’atath goes on and on about Wrath doesn’t she?
I suspect Xal’atath and Xe’ra to be the Stonewright utilizing the Enemy Infiltration Preface plan to infiltrate the Light in a way that hides her corruption.
First she becomes a Night Warrior then she allows the Naaru to encase her in a Naaru Prime shell using the Night Warrior power she is channeling from Elune to keep herself in control. Then she implants herself into the Earthmother’s Eye Socket until ripped out alongside An’she for causing the Naaru assault on Revendreth(yes the Earthmother is the true Stonewright).
Then she gets gifted by her brothers to the Old Gods and arranges for her physical body to be encased within a custom made Naaru Prime.
Once the Naaru Prime is blown up by Illidan she returns to the Night Warrior’s Realm the Void and takes the form of a Void Naaru and rushes over to Eredath and infects it impersonating L’ura who had long become the Void Revenant Nhal’athoth(explaining why it’s remnants resemble a Naaru).
She gets her body eaten by Alleria then returns to the Void of Night then after letting herself get injured uses her Dagger Form to ingest enough Souls to gain the right amount of Death to return to the Shadowlands to impersonate the Stonewright who slumbers within Beledar and yet utilizes the power of Elune to send her roots to the Black Blood! The Haranir do resemble the Venthyr you know.
Since Xal’atath no longer has a way to filter the Shadow thanks to Alleria she simply has to wait until the Stonewright uses those Roots to absorb the Shadow to kill An’she forcing him to sever his connection to the Stonewright.
The Shadow will be painful(due to the Light pollution infecting Xal’atath) and give the Shadow entry to the Void(which was polluted with Light and Death) but Xal’atath will gain the Earthmother’s Soul one way or another.
Alleria will find out that Xal’atath’s Void is not Shadow just by discovering the Dark Heart she broke and attempting to draw on it’s Void only to feel pain.
Cue Xal’atath mocking Alleria for letting the Light purify her without realizing it while going into a monologue over how she and An’she infected the Earthmother’s Eye Sockets and how the Earthmother is resorting to that very Shadow that Alleria failed to ingest to purge the Light I.E. An’she from her body!
She will go on to state she infused Galakrond’s Necromantic Energies(resulting from the Earthmother unleashing her Death Magic upon Yogg-Saron/Mueh’zala to corrupt him to Death) into the Earthmother filling her with his Hunger.
She will be shot dead by Alleria(sending her Avatar to the Void of Night even as her true body remains in the Shadowlands) as An’she becomes the Final Boss of the Haranir Homeland Zone while the Earthmother herself becomes the Final Boss of the Azeroth’s Core Zone(the Earthen are digging into Azeroth’s Core for a reason so why can’t that reason be to serve as the Final Zone?)!
Midnight will have Xal’atath upon learning that there is an actual World Soul separate from the Earthmother will immediately hijack the Sunwell through her connection to M’uru and unleash an invasion from the Void of Night while staving off the Void of Shadow’s attempts to use her to invade the Void of Night.
Xal’atath’s High Elven Puppet gets killed in the Void of Night ending her for good and creates a Portal into the Void of Shadow setting up our final confrontation with the Shadow leaving Death as the sole threat which brings us to Ulduar.
Remember Odyn decreed that all Old God works be passed off as Titan Works which is why I suspect that Ulduar is actually Ice Crown Citadel. I suspect the Halls of Infusion is Yogg-Saron’s intended Prison which he escaped when Odyn decided to grab it’s resources to invade Avaloren.
Archaedas would have been the builder who built Uldaman and the Vault of Memory to help sell the notion that the Titans built everything!
Yogg-Saron/Mueh’zala would have returned with Icecrown Citadel Ulduar, appoint Loken as Prime Designate while capturing the other Titan Keepers and the Nathrezim would have headed out and built the Chamber of the Heart and The Last Prison to neutralize C’Thun and N’Zoth who have already breached containment around the same time Yogg-Saron did while simply deciding to stay put.
Ner’zhul upon Archimonde and Tichondrius’s defeats during WC3 would have violently seized Icecrown Citadel Ulduar chaining Mueh’zala with the same tech used for the other Old Gods in the Chamber of the Heart and the Last Prison.
The Last Titan’s Zones will be Northrend Revamped, Icecrown Citadel Ulduar(located under Storm Peaks, Crystalsong and Icecrown), Iridikron’s Lair Harrowsdeep(located under Sholazar Basin and Archaedas’s citadel Wintergrasp), Azjol Nerub(located under Borean Tundra and Dragonblight) and the Depths of Zul’Drak.
Xal’atath’s true self whom we’ve seen in Revendreth will become the Big Bad of The Last Titan fought in the Tomb of Sargeras!