If we do return to Icecrown, it's not gonna be the main plot point. Zereth Mortis is.
This is my assumption: Zereth Mortis is the big part of 9.2, and the Sepulcher of the First Ones is the raid. The finale of each Covenant storyline happens here, as well.
Maldraxxus: The Primus sets up defenses on Azeroth, and we also learn about Helya in Northrend. Something occurs where she assaults Ulduar, and we aid the Titan Keepers + Odyn in stopping her once and for all.
Ardenweald: We go to the Plane of Life (1 zone. Prolly the size of one of those Legion invasion points on Argus) to meet up with the Winter Queen's Sister. The Dreadlord infiltrating there + The Mawsworn attack, and it ends with Elune, the WQ, and "An'she" teaming up at Zereth Mortis. "An'she" meets Baine Bloodhood, and Life/Death are together in this conflict. Bwonsamdi has a lil arc involving Vol'jin becoming a fully grown loa, and we may find a Varian cameo here.
Bastion: Uther explores the Maw to find Arthas and other things to aid in the cause against Zovaal. Uther and Jaina meet the soul of Arthas, Arthas says what's up, and dips. Uther and Jaina find clarity and completion in their arcs finally.
Revendreth: Renathal and the Harvesters continue their search for Denathrius. All of this leads into 1 final confrontation against the fallen Sire at the Ruins of Nathreza, where Denathrius either falls 1 last time, or decides to return to his fellow Eternal Ones.
Main Plot: Mainly focused on reaching Zereth Mortis, establishing a foothold there, going to the Sepulcher's Location, going to Sargeras' blade and figuring out what caused the drought to begin with, and going to the Halls of Reflection or so to figure out how to save Anduin's soul, and for Sylvanas to truly realize her destiny.
World Boss: Mawsworn Galakrond. Freed by Zovaal at the hidden Depths of Torghast, the soul of the monstrous Galakrond has risen again into a being of pure dread and horror. Fueled by the countless stream of souls within the Shadowlands, this former Proto-Dragon shall not rest until all of Reality's consumed by its constant hunger.
Raid: Sepulcher of the First Ones. This raid consists of First Ones technology and architecture, while also consisting of massive facilities representing the 6 Cosmic Powers. One facility looks akin to Ulduar, one facility looks akin to Antorus, one facility is of Light, one is of Death, one is of Shadow, and one is of Life. Each Facility consists of 2 bosses each, with Zovaal being the final boss. 13 bosses.
Or at least, this is what I want to see from the Sepulcher. Would be like Ulduar, but of each Cosmic Force.
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So, you basically got a 13 Boss Raid. Potentially 7-9 Chapters of story, MAYBE a Dungeon if they want to do that, 1-2 Zones (I kinda hope Zereth Mortis is like Argus in a way), maybe some Azeroth invasions, and a new World Boss.
Seems good enough. But judging by 9.1's size...
9.2 could be really big, but idk.