I disagree, its a party. There isn't going to be some magical story that is revealed or anything, it will just be sex, cause its party. I doubt its going to be much more than that, cause that is not this type of story. The story are the characters, which many will be lacking at this party.
And why have Lena mention bringing us in game, if the dev is not going to follow through.
You say more important things, I also disagree, there are many thresomes,even the first mmf threesome that has been teased for the couple or even some ffm. Maybe Ian gets interactions with Ivy or Jess. Maybe some side fun. Ian could bring a lot to the party.
But since you brought up ch.12, lets discuss that. Lena still had a small POV in that chapter and when she didn't she was largely a part of that chapter. What about this chapter, absolutely nothing for Ian. Nothing at all, seems unfair and not equal treatment, after Lena got a bigger ch.13 than Ian too.
It just not a good decision in my mind when you have two mc's to have a chapter only have anything going on with just one of them and completely neglect the other, especially with long releases.
And we come back to the main point. What does Ian enjoyers, or people that have Lena in relationship with him or Holly or both, and others have to look forward to? Absolutely Nothing. Waiting all this time for a chapter with nothing, just to give a bunch of stuff only to Lena that involves a couple characters, cheating, or single. This party will last 2 minutes and be not much else.