To keep this thread alive during Wanda's enforced hibernation: This article on the Disney+ service mentions the WandaVision series and when the actors found out about it.
Disney+ would be Marvel’s chance to tell more of those stories. In April 2018, when the cast of Avengers: Infinity War was in town for the film’s premiere, Feige convened a meeting to talk up his ideas. His audience included Tom Hiddleston, who plays Loki, and Elizabeth Olsen and Paul Bettany, who portray Wanda Maximoff (aka the Scarlet Witch) and the Vision. Among other ideas, Feige laid out his plans for the Loki series and another called WandaVision, focused on the other two characters, who are romantically entwined. Everyone, he says, was stoked.
Feige was more nervous about his pitch to Jeremy Renner, who plays The Avengers’ Hawkeye. Marvel had a deal for Renner to star in a movie based on the character, but Feige wanted to turn the project into a Disney+ series. Renner turned out to be fine with the change. “He totally got it and said, ‘Let’s do it,’ ” Feige recalls. (Renner didn’t respond to a request for comment.)
He declines to discuss the budget for the shows—including reports Disney is spending as much as $25 million per episode on some Marvel shows, more than HBO is believed to have spent during the final season of Game of Thrones. He does drop one little morsel, though. If you want to understand everything in future Marvel movies, he says, you’ll probably need a Disney+ subscription, because events from the new shows will factor into forthcoming films such as Doctor Strange in the Multiverse of Madness. The Scarlet Witch will be a key character in that movie, and Feige points out that the Loki series will tie in, too. “I’m not sure we’ve actually acknowledged that before,” he says. “But it does.”
I recall that during the press conference for Infinity War Elizabeth Olsen started half-jokingly pleading with Kevin Feige to bring her back. I'm not sure if that was before or after she found out about the series but I do recall Paul Bettany saying that when they called him in for the pitch meeting he thought Feige was going to fire him.
I certainly did think Wanda had a major chance of being retired from the MCU altogether or at least relegated to minor parts, so while there's a lot that could go wrong with her portrayals I'm glad she gets to be a top-billed character in a couple of projects. Olsen is way too good an actress for the undemanding parts she's had in the MCU up to now, so I hope we get to see what she can do.