According to the game's illustrator Mikael Leger, Elijah Kamski was originally going to own a pet android cat, but for unknown reasons, it was scrapped.
Alice was originally intended to be entirely mute, and only being able to communicate with the player using American Sign Language. Concept art of ASL books was also created, as well as a scrapped gameplay sequence where Kara would learn ASL that was intended to also teach players basic ASL signs. The reason for its removal is unknown.
The Conner android has several possible references to the Terminator film franchise. Conner is an "RK800" model, just as Arnold Schwarzenegger's character from the films is a "T-800" model initially. The name of the robot from the game is "Conner" which is very similar to the surname of two central characters from the films: Sarah Connor and John Connor. The Trophy for letting Conner die every way possible is called "I'll Be Back" which comes from Schwarzenegger's icon line from the first Terminator film.
Spoiler:In the junkyard sequence, the original Kara android from the tech demo that inspired Detroit: Become Human can be found among the wreckage in an extremely dilapidated state. She sings the same song that she can be heard singing in the tech demo.
Once you've finished the game and return to the main menu, Spoiler: when Chloe, the android who serves as a guide, asks you if she could be set free, it was originally intended that she'd permanently disappear if the player lets her go. However due to player requests, in an update it was made that if the player had let her go, they could later be asked if they wanted another Chloe android to take her place.
Very early on in the game, if the player makes certain unorthodox decisions in the Kara storylineSpoiler: it is possible to have both Kara and Alice die extremely early. If the player goes to the Main Menu right after doing so, Chloe will slightly break the fourth wall and scold the player for "letting them die". She will then tell the player that the "lives of these androids are in your hands".