Don't remember where I read it but it sounds like Eva may be set to give Marcel more screentime in the epilogue, in whatever form that may be. So it might be beyond most of the brief dialogue we've seen so far. Though I don't expect any sex scenes for Holly with him for at least another few updates, to provide a bit of ramp-up. Maybe the very beginning hints of a path option for Lena, though there has been absolutely no in-game foreshadowing between the two so far, beyond her serious case of Dickus Africanitis Addictus in a select path or two. So that part's anybody's guess.
Of course, there will be the obvious Ivy and Jeremy interactions. Likely some Mark (Club DJ, after all). Maybe Axel, since he was absent from Chapter 11 as far as I can recall, other than a phonecall. Hopefully a surprise guest/stranger, too. Maybe a cliffhanger hint into Gillian's boyfriend or another development Ivy laid out in the far-too-long exposition dump in Chapter 11, like Axel/Cindy, ect.