Do you remember the scene, in the trailer, that ALWAYS shows up at the end of everything else? Like, Goku's all shirtless, something's coming at him, and all? What if that's the Post-Gogeta event? And the prelude to Ultra Instinct? I mean, think about it. Broly's all done, he's tired of Goku (Due to Vegeta being comissioned out of the fight VIA the defusion of Gogeta), he does his Ultimate Move, and it's up for Goku in SSB to stand up against this monster alone. However, that fails miserably, he's all down for the count. Until something happens, and he goes U.I once more. Then, he'll restrain Broly like nothing, Ultimate Battle will play, we'll maybe get the Canon Dragon Fist with U.I, and Broly will be knocked out in the end of the film, but not dead. Hence, Goku will ALSO fall in the end as well, VIA U.I shortening out on him.
"BUT WHY ISN'T U.I GOKU SHOWN IN THE XENOVERSE 2 DLC BS, THEN?!"
Cause 1. He's already in the game. And 2. They haven't leaked anything else besides the new Characters. We'll likely see a new moveset for U.I Goku, as well as a new skin, soon. Idk, though. We might not even see U.I at all in this film, but that'll end up just being a waste of time, in my opinion.