Upon consideration, here's some thoughts:
Northrend TLT
-Season 1-
Borean Expanse (Borean Tundra + Sholazar)
-Sholazar Titan Facility - The true purpose of the Basin's place in the Titan Manifold
-Fractured Nexus - The Titans shatter the blue dragonflight Nexus, causing arcane havoc
Howling Hills (Howling Fjord + Grizzly Hills)
-Utgarde Catacombs - The halls below Utgarde Keep, full of Titan-sworn vrykul
-Vordrassil's Roots - The depths of Yogg-Saron's corruption is revealed
Icecrown Blight (Icecrown + Dragonblight)
-Ruins of Naxxramas - The Scourge still haunt the fallen remnants of the Necropolis
-Citadel Soul Engines - The Titans assess the damage caused by the Jailer's ambitions
---Iridikron's Lair - Raid. Iridikron makes his move, but should the heroes stop him or help him...?
Storm Peaks (Storm Peaks + Zul'Drak)
-Halls of Fire - The volcanic source of Ulduar's power, part of the newly revealed Ulduar substructures
-Halls of Horror - A prison containing the servants of the Old Gods, part of the newly revealed Ulduar substructures
-Season 2-
Northrend Underworld - The region that lies below Northrend's surface
-Azjol-Nerub - The true Spider Kingdom is on the verge of rebirth
---Ulduar Manifold Complex - Raid. The very heart of the Titan Manifold that cages the Worldsoul
-Season 3-
Worldsoul Memory - A realm within the Worldsoul, formed from the memories of Azeroth
-Seat of the Pantheon - Sargeras is free, but his prison may hold clues to stopping him
---Worldsoul Core - Raid. The Worldsoul strives to be free of any who would shackle her
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Goddamn, the thought of the Titans throwing a switch and then huge chunks of Storm Peaks basically break apart and float into the air is hot. I would love to see that, get us real vertical. Get us flying all around there. Probably not flying off to another place or where our city is gonna be (I don't think the Titans are going to be our friends) but that would be a great overhaul of the Storm Peaks, ripping it apart into a bunch of floating islands with Ulduar as some colossal Titan fortress.
I see them as needing mostly new stuff, with maybe revisiting old concepts. Like having Titan facilities beneath Utgarde Keep where vrykul were originally produced. An old WotLK quest has mention of a 'Stoneforge' that I don't think was ever found - the one in Ulduar was called the Forge of Wills.
I think Zul'Aman will be an entire zone, with a raid there that evokes the original raid/dungeon, but delves more deeply into the structures beneath the city (there's a faceless one down there). Agree on Deatholme and Magister's Terrace.