The following contains MAJOR SPOILERS for Transformers: The Last Knight.
The Transformers film franchise is moving forward in a big way regardless of what happens with the new movie. Nothing makes that clearer than the new film's post-credits sequence. While previous final scenes have added little to the overall story of Transformers, the one that accompanies Transformers: The Last Knight will almost certainly have direct implications for the future of the franchise. After a few of the credits roll we get a moment with a strange woman standing in the desert, but as is to be expected, she's more than meets the eye.
First, some background. The new big bad of Transformers: The Last Knight is Quintessa. Like the Transformers, she is some strange combination of person and machine. Though she's also clearly unique, and she claims to have created the Transformers race. She enlists Optimus Prime to help her obtain a staff that had been stolen from her with the promise that, with it, she can drain energy from Earth in order to revitalize the Transformer home world of Cybertron. We also learn a vital piece of information. That Earth, is, in fact, Unicron, a planet known to be the ancient enemy of Cybertron. Several metallic horns begin to unearth themselves on the planet whose purpose isn't entirely clear, but is clearly part of Quintessa's plan.
In the final battle, Quintessa is blasted off of Cybertron's surface and what happens to her is unclear. Her plan has been thwarted so things would seem to be ok. However, after a few of the credits roll, we cut to one of those Unicron horns in the desert. One of the people investigating the horn approaches a woman standing near it. She's dressed in blue and she tells the man that she knows how to rid Earth of Unicron. As she speaks a shimmer crosses her face which reveals a sort of framework beneath her skin, which resembles the structure of Quintessa's face. Quintessa lives, and she's up to something.
Her statement would appear to be an attempt to help humanity, but based on the fact that she had been willing to destroy Earth earlier, we can't take it at face value. We can't even be sure that her goal in this film was actually to help Cybertron. Instead, we're guessing that since her initial plan, whatever, it was, has been foiled, she's moved onto plan B. Also, the fact that she can take human form means that nobody will even know that she's out there at all. We've seen Decepticons take human form previously and while that seemed somewhat random at the time, the fact that Quintessa can do it as well may go some way to explaining it.
Fans of the classic 1980s Transformers have been waiting to see the Unicron for some time. He's the villain, voiced by Orson Wells, from the original, animated, Transformers: The Movie. The reveal that Earth is, in fact, Unicron is a major twist on the original version. However, Quintessa's statement that she can help kill Unicron would seem to confirm that he isn't just a planet, but a being of some kind. If he can be killed, he can likely also be awoken. We're guessing that killing Unicron isn't Quintessa's true goal. Even if it is, what kind of movie would the next one be if she succeeded?
We likely won't get a clear answer for awhile. The next Transformers movie is set to be the spinoff focused on Bumblebee which will be set in the 80s. It will likely be a standalone story without much connection to the proper movie storyline. Having said that, the introduction of both Unicron and Quintessa open up both a past and a future of the Transformers that will very likely play into future movies. We know that a lot of work is going into expanding the Transformers into a larger cinematic universe and this final scene is the beginning of that expansion.