This is one of those moments where VFX technology is driving narrative features. Usually, someone cooks up the story and then the VFX people have to figure out the magical bullshittery to make it seem real. In this case, however, I think we're seeing the recognition of the potential of state-of-the-art VFX tech to inform the narrative.
Remember the Abyss? That's OK, no one does. But the visual effect of the "water alien" in the Abyss directly shaped the design (and avowed properties) of the "liquid metal" Terminator in Terminator 2: Judgment Day. Without the Abyss, you don't have effect. James Cameron developed the effect and then determined how to reuse it in another film. In effect, the cart driving the horse.
I think this trailer is the same thing. Remember Logan where old man Logan has to fight young man Logan? Remember how blown away people were by de-ageing effects on Ian McCellan and Patrick Steward when they did the Dark Phoenix story? Well, we now have the effect, so that, in effect, offers a narrative opportunity. Will Smith can fight the younger version of himself (the one we used to know and love). I think someone finally said, "Fuck it, these deaging effects are so good, why don't we just make a movie with the young Will Smith?"