You know, I remember my first
impression of this series is that this is just a twisted degrading parody of Imaizumi. (Obviously, my opinion of this series has changed since then, lol...).
But anyway...assuming this 'one-time only' 5P plan blossom to something else, I could see Moka being uh, open-minded enough let the trio continue having sex with Ueno if both parties are interested in it. I mean assuming everyone will have successful careers in both the law (Ueno, Kanako & Chisaki) and economic ( Tsubomi & Moka) field in the future, they need to find one way to blow off some steam from their stressful jobs, lol.