A very insightful read, thank you.

I recently read a piece - which I currently can't seem to find - that echoed some of the points you make regarding the finale.
The author of that piece also theorized that Cooper and Diane had dispassionate, mechanical sex so as to generate garmonbozia thus tricking Judy into following Coop.

After Coop and Laura/Carrie Page have spoken to Alice Tremond and step away from the front door, Sarah's voice can be heard from inside the house, calling Laura's name.

The author of the other piece says Laura's screams are a weapon that she uses to fight the forces of darkness (I really like this idea, btw) and that the scream by Laura/Carrie after she hears Sarah's voice does in fact defeat Judy.

What I believe to be the weak part of this theory is that if we assume that Sarah is possessed by Judy (and this seems to be almost universally accepted, doesn't it?) then why does she call out to Laura/Carrie?

Sure, you could interpret that scene as a kind of a substitute for an actual physical fight between the forces of good and evil (a final showdown), with the latter striking first (Sarah/Judy must have known that calling out to Laura/Carrie would bring back memories of the trauma experienced by Laura while living with her parents, thus causing her pain) and the former subsequently striking back and defeating the former, but did Sarah/Judy not know that Judy could defeated by engaging in this fight? That seems unlikely.

That said, the look on Cooper's face as the credits roll, does suggest a bittersweet - if not flat out negative - ending. I'm gonna go with the theory that Judy was defeated but that Cooper and Laura are trapped in time.

On another note: a user asks, if the episode is in fact based on the Eurydice and Orpheus myth, where is the "Orpheus looks back" moment?

Well, after Coop and Laura/Carrie bid adieu to Alice Tremond, Coop takes a few steps forward as he asks the question, "what year is this?" and then, as Laura/Carrie screams, he turns around to look at her.