(Edit: it's fine to Animal Crossing Bells downvote this if you're a avid TTer and do not wish to mark spoilers or something. Just trying to provide another viewpoint in this thread that is asking for feedback)

The things which produce my Reddit feed and top the listing on sexy after the tacky have been varied on subject so I would not say there is an issue with common occurrences that neighborhood upvoting and downvoting doesn't already solve.

I generally think spoiler tags are silly, but you'd want to go farther than just time travel in the event that you really wanted to prevent spoiling things people have not seen yet. All out of current season content will require a tag weather it's an old image from the image library or even a fresh picture from time traveling both will show new gamers thing they haven't already seen. Plus things like the latest direct video clips would require tagging because it reveals new content before anybody gets a chance to see it in-game.

I really don't see any problem with memorials. I think remembering your loved ones is beautiful and shouldn't be judged as Nook Miles Ticket For Sale something dark or scary.