I strongly suspect that we will get to see the MC.
Before high school:
Neil had a legal battle at one point. Maybe we'll learn more about that as well.
High School:
We know how Zoey and the MC met. But what we don't know is how the parents' lawsuit was averted by the bully the MC beat up. The charges were averted, so no lawsuit. We will also certainly learn how Zoey and the MC became closer. Why did Zoey go to San Diego before, or how could Zoey go to San Diego before? Simple. Zoey is 1 year older than the MC. Josy lived with her father during her senior year of high school. This is where the events overlap. The MC is still in high school when Zoey goes to San Diego. Now Josy comes to the same high school, but never meets Zoey. The breakup between the MC and Zoey was not long ago and the MC was also not sure if it was love or not. The MC doesn't want to jump right into the next relationship. Josy is in a relationship with Maya and we know that Josy is faithful in a relationship but that she doesn't talk about that relationship. Josy and the MC probably run into each other all the time at school, but don't notice each other. That only happens when they both work at the store.
But what does this have to do with Zoey now? Zoey is a year older than the MC. What if Zoey just wanted to take a year off and then go to college with the MC? Then Zoey meets Josy's mom in San Diego as she's getting a tattoo. They talk at length and find things in common, like Josy goes to the same high school as Zoey. Now Zoey meets another man and falls in love with him. Contact between Zoey and the MC breaks off. But Zoey's new relationship does not last. Suddenly she sees a video of Tremolo on the Internet, as he gives a concert with Jill. Old memories are awakened and Zoey goes off to college.
In my opinion, Interlude will answer some questions.
How did Tommy end up at B&R? (This question is not really important).
Josy was not accepted to B&R in the beginning. And why? She's actually the perfect college girl.
Surprisingly, she does get accepted to B&R. But why? Was she on the phone with her mother? Is Josy's mother and/or Zoey the connection to the rich and powerful in the BaDIK world?
DPC himself has written that he is also doing the interlude to clarify some issues and not just for technical reasons. It is also to answer some questions to better understand EP9.