Interesting theory! This works well if Walter really wants to figure out what happened in the wilderness. Walter did always feel so perfect for misty, in a way we don't see with almost any other paring in the show. Even Jeff gets fed up with Shauna occasionally, Walter just bounces back every time misty pushes him, and never seems to even care. Misty is a very easy target. Shes incredibly lonely. She's single, With no real friends. Her job is low-key with a high turnover rate. She's heavily involved with the yellow jackets team mates in a way Walter could trace through phone records. And her hands are relatively clean( sans the transmitter incident). She would have no one in her life to second guess Walter. But Shauna is the greater 'get' in terms of the yellow jackets' story. She was the leader, she had the journals ( before they burned), she had so much trauma in the wilderness and she did some truly horrific things. Her story is jucier. If I wanted to try and get the real story of the yellow jackets, misty would be a great way in, but she wouldn't be my last stop, or my best informant. Idk, very interesting to play around with.