Usually the halfhearted "yay" is a kind of like filling in a bingo-square, like if the stuff we're reading calls back to an earlier, unrelated episode.
As an example, if in the future we're reading some fangirl post and she mentions the Omegaverse in a discussion not otherwise talking about it, it'd probably get a quiet "yaaay" from someone.
Like "Yay thanks for reminding me."