It's very seldom thata we see fancastings ultimately evolve until actual castings. In the case of Rosario Dawson, it worked.
In a recent episode of the Disney+ Star Wars series, The Mandalorian, actress Rosario Dawson made her first appearance as fan-favorite character Ahsoka Tano. This marks the first live-action appearance of Tano, who only appeared in animated form on The Clone Wars and Star Wars Rebels. Dawson's casting was rumored last year and confirmation of it eventually leaked.
In an interview with Vanity Fair, Dawson revealed her casting materialized after she retweeted a fan casting of her as Ahsoka Tano from social media. As it turns out, the fancasting caught the attention of Lucasfilm.
She explained, "Actually it first came from fans online. Someone tweeted me and fancast me. I retweeted back and I was like, ‘Absolutely, yes please' and '#AhsokaLives.' And apparently that got the attention of someone who has been doing the Star Wars press for years. She forwarded it to Dave Filoni. That kind of started a whole thing.”
Once The Mandalorian executive producer executive producer Dave Filoni saw the fancasting, he kept it in his back pocket, which ultimately led to Dawson's casting as Ahsoka Tano before the Star Wars spinoff series even premiered.
The Mandalorian's second season is currently airing on Disney+.