Following the events of Guardians of the Galaxy Vol. 2, Nebula became one of the Marvel Cinematic Universe's most popular anti-heroes, but when we met her in 2014's Guardians of the Galaxy, she was a full-blown villain (who was loyal to Thanos without question).
That's reflected in this awesome piece of concept art from Andy Park who explains that he delivered this take on Nebula at an early point in production, and used the Sith Lords from Star Wars as his main source of inspiration. He explains that he, "didn’t know much about Nebula yet so I imagined her as being essentially a Sith Lord."
It's a cool take on the character, and definitely one which would have worked on the big screen.
Ultimately, Marvel Studios went down a different, but still very similar route, though it is hard to wonder how different the character might have been had James Gunn chosen this version.
Check it out below: