Edit: Added TLDR at bottom
I’ve been enjoying everybody’s thought and theories on this wonderful show since the beginning so I wanted to share mine. I may be wrong, but that’s the fun of the weekly show format.
First off, I believe that while Agatha may be an antagonist, she is NOT the Big Bad. If anything, I don’t believe there will be a big bad, unless you want to count grief or life.
Agatha came to Westview after sensing “a strong disturbance in the force,” if you will, and has been trying to get to why Wanda is doing what she’s doing. She’s been testing her powers throughout to try and get a handle on who this strange magical person is who kidnapped a whole town. In the last scene of episode 8, she seemed truly frightened of what Wanda has become, and worse of all, how emotions are completely controlling her actions. The key line is, “You don’t know how dangerous you are!” That’s not a line of a villain. To me, that’s the line of a protector. Only reason she has the “kids” hostage as that’s the only way Wanda won’t simply blast her off the face of the Earth. Agatha may want to get rid of Wanda, but it’s for the greater good. I believe Vision will end her threat early in the episode, but not kill her. She could be the voice of reason throughout.
That leads to my second point. While there is strong similarities to “House of M” and other X-Men comics, I believe that is not Feige’s aim. The story he and Marvel are telling, IMO, is their version of “The Dark Phoenix” saga, with Wanda in place of Jean Grey. I don’t believe it will end as tragically as that story ends, but there is strong hints of it throughout, with SWORD representing the Shi’ar race and Vision as Cyclops. White Vision (or Plan Omega from the comics) is SWORD’s last attempt to stop the insanity. Monica, Darcy, and Jimmy would be representing the other X-Men. Agatha could be Prof. X in this scenario, but I admit that could be reaching.
Third... as others have predicted, I am pretty sure the secret cameo that Paul Bettany has been eluding to this whole time was himself. He was being cheeky with the media and the fans. And I would prefer that. It’s too late in the series to bring in a Doctor Strange or a Captain Marvel type character without it feeling too much like a Deus Ex Machina. The stage is set for the finale and to bring in someone at the last second would be disastrous to the story. Wanda must end the events herself if there is to be any chance of growth. Of course, that doesn’t include any post or mid credit sequence as that is just to tease the next or a future Marvel project.
However, if there was someone being brought in at the end that won’t hurt the story too much, my guess is it could be Nick Fury to help clean up afterwards. Only person I can see working.
I believe the show will end with Vision begging Wanda to destroy the hex to save what little sanity she has left, knowing full well it will lead to him and the kids being wiped away, like a Thanos snap. Wanda will go off with Agatha so that she can learn to better control her emerging powers before another incident can happen. It’s a depressing end but I feel fits the story beautifully.
These are just some of my thoughts. I wanted to get this down in writing before the finale airs so I can see how far off my theories are afterwards.
All in all, I’m going to be sad when this show is over. I don’t think Falcon and Winter Soldier can hold my interest as much as WandaVision has. I don’t see how it can, but I have faith in Feige and the MCU in general. If anyone can pull it off, it’s them.
TLDR: Agatha is not the big bad, story is more Dark Phoenix than Hose of M, secret cameo is either Paul Bettany or Nick Fury, and Wanda leaves with Agatha at the end.
