I would have guessed a real expansion would have seen Neyrelle grafting on Lilith’s Arm or something which allows her to open the gates to High Heavens and Hell. She is all emo trying to save her Mom from damnation.
You would go back and forth between both realms trying to bring stability to Sanctuary and there would basically be some sort of mechanism for Stability to where you can only spend so much time in either realm before you have to flip to the other.
Too much time in Hell, you gain Corruption and too much time in Heaven you gain Purity. Once you reach max stacks, you stop gaining rewards (similar to Whispers) and have to travel to the other Realm.
Hell Tides get replaced with Purple version where both Angels and Demons come out and tear everything apart. They not only fight you but each other.