I could easily imagine an adaptation choosing to run Part 1 and Hivebent in parallel, sacrificing the shock factor of "the internet trolls that have been hassling these people are in fact actual trolls from space" in favor of making it a big reveal that "oh shit time travel" well in advance of Dave entering the medium. This would simultaneously help smooth out the pacing of the early acts in adaptation, and also would be structurally closer to how Act 6 tends to roll.

That said, it's equally plausible that Jade Karkat and AH might just not be in the pilot to begin with, and are in the trailer because they've already gotten substantially far in animating Part 1.