Isn't this potentially a perfect love triangle? Hiyama loves Sayoi, Sayoi loves her sister Satsuki, and Satsuki is fond of Hiyama? If this is a polyamory ending, would it still qualify as yuri because there are two ladies involved, or does the man ruin everything?
I don't really mind either way this goes because I trust the author. But I get the impression they're the seat-of-your-pants type of author who will steer the ship into a new direction on a whim if they think it makes for a better story, or if their impression of the characters has changed. Sometimes shit endings happen because authors follow the ending that was written in their outline even though over years of writing the characters went into a different direction. It's still waaaay too early in this story's life to predict anything.
No watter how it goes, it's a little unkind to accuse Harushion of writing "yuri bait" knowing that she has delivered the goods in the past. You can trust that if she does go for a hetero ending, it's because she genuinely felt that it was the right one, not because she didn't have the ovaries to follow through on the homo. You've got to respect that.