VI's storyline is excellent
I hope the storylines of the other three important characters - two stepsisters and stepmom - will be just as compelling as hers
If the other three main characters were to engage in sexual relationships with other men at this point, we wouldn't feel the same intense emotional/sexual impact we experienced with VI's storyline. This is because we haven't yet developed the same level of intimate and emotional connection with them. It would lean more towards Voyeurism rather than Netorase, and I think we all agree that Netorase > Voyeurism
For instance, if in the next update Anya is to engage in sexual activities (such as blowjob or otherwise) with another man, it would be more effective to structure it where she first shares such moments with MC in the first half, then with the other man in the second half. This way, you can fully experience the sexual/emotional tension and excitement