When Optimus Prime flew into space at the end of Age of Extinction, fans suspected we may get to see Unicron in Transformers 5. Now that sounds like a possibility as some potential storyline details have come out.
According to Dark Horizons, one of the Transformers voice actors revealed where the story would be going in the fifth movie:
“Now, voice actor Mark Ryan has reportedly revealed that the upcoming film will go in two distinct directions. Ryan, who voiced the characters of Jetfire in the second and Lockdown in the fourth film, appeared at the UK’s Wings and Wheels convention where he said the first storyline will follow Cade Yeager (Mark Wahlberg) as he and both the Dinobots and some of the Autobots set out to save Earth from an impending threat.
The second will lay the groundwork for the future of the franchise which will focus more on the Autobots and Decepticons themselves. In that second storyline, Optimus Prime heads into space to find the creators of his race – a group known as the Quintessons. Optimus will also confront the giant transformer known as Unicron.”
At one point Unicron was rumored for the fourth movie, so it’s possible he’s someone they’ve been planning to use for a while. Hopefully he is the giant planet-sized robot he was in the 1986 animated classic.