No, there isn't. With a very large stretch, NTR can be considered sex between Josy and Maya in episode 5, but the player in the friendship path doesn't see it. The doctor has already shown himself to be enough of a chicken when he made Zoe cherish her pussy for a year for the main character's sake.
It means nothing at all. I assume that Sage has some sexual preference for BDSM. In episode 9 she liked the MC choking her, liked anal, liked sex in the basement. She also liked being watched when she fucks.
Also, I don't think he would create separate scenes for that choice. I assume there will be something similar to scenes 50 or 100% that depends on MC's choices at the end of episode 9. Also, if tDPC was really planning the MMF, he wouldn't have made up clones, he would have just made renders with certain characters, which suggests that DPC wasn't sure about the audience's reaction.
And most importantly. If he did that, Sage or Isabella would just be hated. You're very much understating the importance of the anti-NTR community. The authors of Redfall had to remake the game just because the main character's mother had sex with her own husband there.