If adding a canon/non-canon Christmas scene is what they enjoy then I don't see any problem.
hard to disagree with that. on anything.
but I just don't see the point in non-canon events. it just seems like the even worse version of "then I woke up and it was all just a dream". scenes should have consequences for your characters or they should be cut.
writing a christmas event into your actual story makes it a vastly better version of the event. doubly so when the story is based on doing things you shouldn't be doing, like is the case with 99% of sex stories. so in your story the aunt was never supposed to do anything with you, but in the christmas party she gets drunk and blows you in a closet. you go back to the main story and it never happens again, but you have all the guilt and hidden secret and threat of it being uncovered to bounce your writing off. doesn't have to be incest, could be anything like the aunt fucking your dad or anyone she shouldn't. that only works if the deed still exists in the morning.
anne's point about showing scenes that aren't yet justified in the canon progression I don't get either. it's just another way of losing all the tension you worked so hard to build up. it's like starting a joke with the punchline, the quickest way to ruin the joke.
MAYBE do it after you've completed your game, as a bonus. but never undermine your story by giving up the goods early or undermining your characters by making them break their character. it just diminishes the impact of your story, why would anyone do that.