Kate Winslet was so keen to return in any capacity as either a "flashback or sim[ulation]" that she got her agents to get in contact with producers to specify her availability. However, it was the producers who turned down the opportunity for the sake of time and storyline constraints.
Like many other adaptations of young adult novel series (Harry Potter, Hunger Games, Twilight), the plan was to split the last book in the series (Allegiant) into two films, with this movie basically covering the first half, and Ascendant covering the rest. However, due to negative reviews and a disappointing box office result, it, along with a TV series follow-up, were subsequently cancelled.
Drones are supposed to be controlled with one's left hand. However, Christina is the only character who controls her drones with her right hand, due to Zoë Kravitz being left-handed.
Despite the film's cliffhanger ending, there won't be a sequel to put a definitive ending to the story.
Tris' hair was supposed to be chin length in Insurgent, so in this film, her hair is true to the book.