Well, I would love it if Nya'lotha was EXACTLY like how it was portrayed in the Warbringer...a city of pyramids and zigguarts under an eternal low sun, the glare blinding anyone who looks up. At the edge of the city, black against the sky would be the massive bulk of N'zoth himself. N'zoth would be the raid, as he is just too big to actually fight directly.
The raid would begin when the goblin cannon, which we STILL haven't fired as promised, is used to blow an opening in his carapace. I can imagine part of the raid would take place in the city, then we enter his body and fight our way to his core/brain/soul/essence. That would be the final boss.
That's what I would like to see.