As per the book The Story of Marvel Studios (via /Film), the Wasp was written into The Avengers when it was a possibility that Scarlett Johansson wouldn’t be able to reprise the role of Black Widow due to scheduling conflicts. Producer Jeremy Latcham explains:

“It was all about The Wasp. He wanted to cast Zooey Deschanel. [Wasp] was the funniest character in the whole movie, and well-written.”

Avengers director (and now cancelled) Joss Whedon also said about the Wasp:

The Wasp happened because there was a short period where it looked like we weren’t going to be able to get Scarlett [due to scheduling conflicts], so I was panicking. I thought, ‘Hold on, we could do The Wasp.’ Then I fell in love with that. But we did get Scarlett, and then I realized I had written this entire movie about The Wasp. Oops. I overcompensated there.”

There isn’t any reveal on whether the Wasp would have been Janet or Hope, but I think Deschanel would have been a great choice to play the character, especially with how big she was getting around the 2010s. For now, Deschanel has sort of focused more on her TV career, but I have no doubt that she would have been a fantastic Avenger.

For now, Marvel Studios is setting up for the release of Eternals on Nov. 5. The Wasp returns in Ant-Man and the Wasp: Quantumania which comes out July 28, 2023.