It would be interesting to see a jealous Sophia.
Not the beginning of jealousy that we could see during the Chiken-fight but a jealousy which makes Sophia aware that she cares more for the person than she expected and why not act of her own will and do something hot to show:
You do not touch, he/she is mine.
If we envision an ending on Filthy Route where Sophia ends up with another man/woman, it won't be one of her children or Sam or Zach, that would be illogical.
Even the little trip to the pool with Sam was a bit (to please him).
Sophia would end up leaving her husband to go and live with another man or woman of her age.
What can she hope for with a young person in her children's ages? nothing.
Again this is only my opinion.
It would have been the most the plausible ending but the only reason why I am not sure about it is because Sophia has children. She won't just abandon them and go away with someone else. At the beginning of the game it is said that she loves her children a lot and will do anything for them, which is pretty evident even throughout the game.
Also the fact that she will have a much more intimate bond with them by the end. With Ellie it should be fine but I am afraid of how to go about Dylan after having sex with him. Personally speaking every single guy in the game is despicable except for Liam and Carl.
I really don't understand how exactly he will conclude the story, the biggest reason for that is that we don't know how corrupt is he going to make Sophia. Does L&P want to push her down to prostitution or just an unfaithful wife, or something in between. Till that is not known, predicting the end is really difficult.