I personally hope for a path where normal Ian and slutty Holly finally become a dedicated couple. As you said, the main point of Holly becoming wild and slutty was that she believed Ian was not interested in her shy self (even if he was). So she took Lena/Ivy as examples and became a wild one herself. That we can flirt with her on the beach and tell Holly how hot she looks and how nice she is, gives positive points with her. So it looks good that there will be a path for Ian and Holly to become a couple even this late.I'd be surprised if that doesn't happen. I think slutty Holly will want to prove she's the equal of Lena, and can seduce Chad Ian. The whole point of her becoming 'slutty', was because she couldn't get Ian interested in her. So now she's becoming more Lena-like, she'll probably want to scratch that itch.
Some time ago a currently unused, but in the folder, pic was posted with slutty Holly and Ian having sex together. And this pic would have very much fitted the scene where shy, but encouraged Holly and Ian deepen their relationship. So there is hope for a wild Holly/Ian couple.
But I also agree with you that there will be most probably a path where slutty Holly and Ian have at least a fling.