Think like a Developer:
You're remaking a visual novel that everyone who's 25+ loves. That lots of people tried to re-do but none did to the end. You was able to fetch attention to the Remake, and the routes everyone wants the most are Kouya, Kyouji and Soutarou and Torahiko, the last three never had their routes finished.
Torahiko is also the "main route" of the game.
If his route is finished, there's a huge change most people would lose interest in the game. So it will obviously be the last one. I believe Torahiko itself will be the last route to be added and will also only be added once all artworks for his route is complete, because once his route is done, the game is also done. But I may be wrong.