I mean they could explore Chloe and Max as gradeschoolers or "The Max Caufield Chronicles." Follow the gripping introverted life of a girl who goes to highschool in Seattle and doesn't socialize. Experience life un-changing moments not worth bringing up in previous games. No superpowers! No adventure!
Or better yet, follow Max as she hangs out with Warren, tries to get over the grief of losing Chloe and deals with the existential dread of being the only person who knows these supernatural things happened.
Alternatively you could just follow the ending where Max decides against Chloe's wishes to let her parents and almost everybody in town die. What once was a genuine relationship would become a guilt driven obligation to somebody who is all you have left Chloe. I'm all you have left Chloe!
Yeah, I think it's safe to say that the best and second best stories they've done with these characters have already been done.