So yeah, I've been reading up on info about the mainstream comic book version of Wanda. As you all know by now, she's not Magneto's son but an orphan raised by magical people in the usage of Chaos Magic.
Chaos Magic was used by Chthon when he governed the world.
Chthon possessed Wanda twice over the course of the comics because of the great usage of the Chaos Magic.
Here's my theory : In WandaVision, Wanda is really distraughted over the loss of Pietro and Vision and creates this warped fantasy perfect reality to live in. The problem is, she uses too much power and because of that, will draw out Chthon and he will possess her.
And when that happens, the combined power will be used to rip holes in the Multivers, wreaking all sorts of havoc, leading to what happens in Spider Man 3 and Doctor Strange 2, which could have focus on Wanda/Chthon and Doctor Strange's plan to save her.
Only problem in my theory is that Wanda's powers come from the Mind Stone, and not Chaos Magic. But they could retcon it ...