Bit of a hopium from this point onward. I'd suggest being up to date on 2.8 leaks before reading.

I'm gonna guess 2.8 is gonna tie in to three specific 'events' considering the people joining the adventure, (something which I guess is also happening to Kazuha's story quest):

1.1's Unreconciled Stars ('Sky is fake', accompanied by heizou screenshots), 1.6's Midsummer Adventure (Alice's bigger scheme as to making an entire set of islands and revamping it) and 2.6's Iridori Festival (Kazuha and Scaramouche information as well as nudging the player character into Sumeru).

Most notably, some randos get in like Xiangling, Xinyan, Yunjin as well as Nahida. The latter, particularly, is a clear standout assuming you've read the leaks. Xinyan has been through the space-connecting doors from Labyrinth Warriors, but it remains to be seen what she's there for. Yunjin, uhh. Mihoyo loves her I suppose. Jk, I actually have an idea.

GAA is, by theory, a special island only allowed entry by those approved by Alice. Yunjin, Xinyan and Venti are all skilled in the arts, while Fischl, who might be Klee's friend, might be invited to be the main 'characters' of the event. Considering how Fischl also has a skin (and how skins don't usually appear out of nowhere), she might be playing a Princess role in a play made by Alice. What Kazuha, Xiangling and Nahida's reasons being there for are currently unknown, but I have an even more outlandish theory.

Alice is recreating the scene what the original Fischl in the book goes through. Volume 0 mentions some special characters: Beast of the World: Gesamtkunstwerk, an opera writer. Zarathustra, a philosopher.

"Once Gesamtkunstwerk takes the stage in the opera theater of the apocalypse, many more Beasts of the World that reside within the center of the universe will inexorably begin to appear as well."

"It is said that those who are highly skilled in the magical arts will possess their own unique domains of consciousness. Their loves, hatreds, yearnings, jealousies, adherence, and passions of the soul will be stored here. In the fictional tales of other novels, this space is called Summerland. The Sommernachtgarten of the Prinzessin is something in this vein."

The Suspected Eternal Return: "But as the universe entered its denouement and all things within it flowed into the Immernachtreich, she spoke another line of enigmatic intent— "Find meaning somewhere. The night deepens."

"Find meaning somewhere. The night deepens, but the dream lives on."

Sounds familiar eh? Alice might indeed end up replicating the last few moments of destruction of the Immernachtreich. But with two archons and an agent of chaos in the midst, will it truly only be a replica, or will it be a vision of civilizations long past?

Considering how there was no mention of an Archon Quest or GAA's quest that makes it permanent, they might do what they did for 2.7 and make the event quest permanent as some sort of archon quest. Akin to how the interlude quests act as extra story content for Xiao and Shenhe, this might be extra story content for our beloved chuuni. Or perhaps something more... It would be wild if this was Sumeru's prologue.