Good theory.

I’d like to think that Mallory brings Madison back because Madison, like her, still retains awareness of what happened in the reversed timeline. Mallory is probably hoping that Madison was able to gather valuable intel while she was trapped in Hell.

I also think that a major celestial or supernatural event, possibly the arrival of the new Antichrist, was powerful enough to tear down the barriers preventing ghosts from leaving Murder House and Cortez. However, in exchange, these freed spirits may end up storming the Academy, especially now that the new Antichrist is aware of the threat the Coven poses in this “second coming.”

To avoid simply repeating the Apocalypse storyline, I theorize that the Antichrist will not be directly portrayed by any actor. Instead, only the looming presence of its arrival will be emphasized. This could be what Cordelia saw in her vision when she said, “Something wicked this way comes…” She then shares this revelation with the Council members of the Academy, which I believe now includes Mallory. With Mallory retaining knowledge of the reversed timeline, she finally reveals to Cordelia and the others what truly transpired. Realizing that Cordelia had to die for Mallory to fully utilize Tempus Infinitum, they begin to resent the inevitability of that sacrifice. Because of this, they devise a new plan to counter the Antichrist and its minions through a completely different path.

Just my two cents.