And here is the spot where someone like Caleb could come into play. Jill had Tybalt, Maya and Josy had eachother, Bella had her husband and Sage had Chad. Out of all the LIs she seem to be the only one who could dump MC for someone else later. Fighting for Sage with some alphadog could be a decent plotline.
First of all: DPC would never do something like that, not in this stage of the story. If this was early on in the game (chapters 1 to 3) maybe. But now that he made the whole community attached to her, doing this plotline would basically mean losing a lot of Sage fans (due to possible NTR implications).
Second: Sage would NOT dump MC for him. After all that they have been through, she now considers him more than just a dick to find pleasure in (this is since episode 5-6 in my opinion, but officially since episode 8). The only instance that this could happen is if the MC cheats on her, but even then I find this difficult to happen.
Just like Jill got rid of Tybalt and M&J sorted their differences out, Sage has also dealt with Chad and is now free to finally get together with MC and explore new sides of a relationship that she had not witnessed before: love and sexual pleasure.
I don't think she needs another conflict to keep the relationship interesting. Her real parents' mystery and Stephen's plot with the prostitution ring should be enough to keep her route engaging.