Dean Winchester's surprise cameo at the end of The Winchesters season 1 episode 8, "Hang on to Your Life" sets up the return of another Supernatural character. The prequel spin-off relies heavily on previously established lore from Supernatural, and while being set in the past may seem limiting, the franchise has proven otherwise. The Winchesters has already featured several cameos, including Gil McKinney as Henry Winchester and Richard Speight Jr. as Loki.
Jensen Ackles, who serves as an executive producer, has also made appearances as Dean Winchester. One major cameo that could occur in The Winchesters is Jack Kline, a fan-favorite character from Supernatural. Jack, being the son of Lucifer and having ascended to the role of God, has the power to send Dean back in time to change the past. Given Jack's love for the Winchester family and desire to fix the mess left behind by the previous God, it would make sense for him to assist Dean in altering their history.
Moreover, Jack carries guilt for accidentally killing Mary Winchester, so helping her live the life she always wanted could bring him personal redemption. Jack's inclusion in The Winchesters would provide a complete ending to his story and offer the Winchester family the happy ending they deserve. If Jack is revealed to be behind Dean's time travel, it would set up a heartwarming and satisfying cameo. Overall, The Winchesters continues to introduce familiar characters from Supernatural, and the possibility of Jack Kline's cameo adds further depth to the story and characters.