Realistically speaking, it would be pretty damn difficult to have a catch-all NSFW system in place on the dashboard. I understand your reasoning, but the difficulty in making it anywhere near effective, along with the fact that the dashboard is a mostly dead site element for most users, puts it on thin ice.
For example, if an entry is already marked as containing NSFW content (take NieR automata for example), the use of the NSFW tag in its galleries is then elevated to content that is considered exceptionally unsafe when compared to the entry's contents. You would also see any images embedded in forum posts or comments, which could just as easily be unhidden NSFW content. Even in the perfect word where media uploads were all perfectly NSFW-tagged and spoiler-tagged, a decent number of items would slip through, depending on the kind of users you're following.
As much as it sounds like a shitty answer, the safest option I can give you is avoid social features of KYM if you're in a position where spoilers or NSFW content would ruin your experience. KYM has just never been in a position to handle foolproof content restriction depending on a user's needs.
