Since UltraPrime posted a video about this, I can say what the spoiler is about, and that "thing":
So, Prime will offer an alliance, but not just with the Maximals, but with the Terrorcons as well. There is something bigger and stronger than them in Peru. Something that the crew described as an "Big Beast" (I'm thinking maybe Predaking or BW Megatron?), so the 3 fractions will fight together in the end battle.
Also there will be a scene where a girl (guessing Elena, Dominique Fishback's character) finds Primal, and he scares the crap out of her lol