Not New Horizons Items if they're an obvious meme/juxtaposition such as Bernie sitting in your plaza, but if you photoshop on wings to your outfit, place a hopeless item on a table, or change the colour of a non-customizable thing it should be flagged so individuals won't be disappointed when they can't replicate it in-game.
I really don't think spoiler tags need to be divisive. At this time it will become an issue since there are no definite rules about what is expected and acceptable from the sub.
If the principles were clear (ie: spoiler tags required for events which have not happened in real time yet or spoiler tags required for articles that contain items which were attained via hacking to bypass timelocking) possibly users wouldn't take it as a personal attack on their play mode when individuals requested they use a spoiler tag.
Rather than feeling sensitive to a sensed conclusion about time traveling it could only be a simple"hey that is against the principles, see sidebar".
(Edit: it's fine to downvote this if you're an avid TTer and do not want to mark spoilers or something. Just trying to Cheap Animal Crossing Items offer another viewpoint in this thread that's asking for comments )