I think the interlude is to flesh out her character before she’s introduced to the main game as a central character.
I personally think it’s a good idea. The interlude that is, I’m not 100% convinced on Zoey. But I’d rather an interlude than having some massive chunk of Ep9 being devoted to her packed full of flashbacks and exposition.
If he plays his cards right and actually makes her a really likeable character in her interlude she can clear up a lot of the other characters behaviour and make the plot easier to write. All game the MC and everyone else has been torn between relationships. “Follow your heart” has come up loads of times. Writing dialogue for every possible combination of girl would be a total clusterfuck. Work would never get done or it would be ambiguous. Like Jill at the end of this episode just saying “dating other people” to avoid having to mention names. However, Make Zoey a common denominator? The LI can have genuine reactions that suit their character.
All these themes spoken about at the start and throughout can be made easier to write if Zoey rocks up and becomes the “other woman” on all routes. We’re too far from the end for everyone to be happily ever after and I think DPC has forced everyone to be with either one relationship or none for a reason. My guess is he’s pruning the branching storyline like he did in Ep4/5 and Zoey is getting an interlude to make her a viable LI and lightning rod for all the individual girls jealousy.