I mean technically he could fix the issue by opening up more routes via side chicks but i'm not sure how that would go over with the majority of fans. Like u said, Quinn, Jade, Riona, Nicole, Camila could all technically get a route if DPC wanted to prolong the game.It feels like he'd have to slow things way the fuck down, either by having each episode take up one whole in-game week but limit the interactions with all main LIs to just once or twice in that week, or make each episode just a couple of days and focus most of the content, particularly lewd content, on a couple of them.
If this game continues at its current pace, you'd expect him to be in an official relationship with Jill by the end of ep 7 or 8 which means no more Sage, Maya, Josy, Camila, Riona, Jade, Nicole, or anyone else except possibly Bella if those storylines continue to stay intertwined. Unless, the MC can continue doing things behind her back like in AL, but I'd wager most people prefer to play the field without consequence until at least 3/4 of the way through the game or close to the end.
More LI's = more time needed to flesh out the story.