That seems like a lot of work for something that still won't solve your problem. If you're really concerned about spoilers in questions — even behind spoiler blocks — from certain sites, then you're better off just not visiting those sites, from Hot Network Questions or otherwise. It's the only way to be sure. With a userscript you can filter the list to exclude sites you find problematic. To summarize:
Spoilerific sites already have (and follow) rules about no spoilers in titles, which is all you see on the HNQ.
Spoilerific sites already have (and follow) rules about using spoiler markup in post bodies.
You're asking for manual use of a meta tag (against SE norms, additional work) to block the question from HNQ entirely (overkill) lest you bypass the spoiler warning and look anyway (avoidable). If we need to do anything, there's a better way than what you propose.
Further, it wouldn't solve your problem. You're relying on users to learn a new guideline and take a special action (some sort of labeling) for reasons that Meta-tags like this are external to their site. It's hard enoughdiscouraged across the network, so getting all users to read and follow the documentation nowdo it here for reasons (e.gexternal to their site is going to be an uphill battle. on- and off-topic lists) Instead, so it's inevitablethese sites rightly focus on things that some won't follow this guideline and you'll still see those questions in the list. Plus you'd need a new mechanism for it; using tags for "meta" information like this is not what tags are formatter to them. Manual, extrinsic meta-methods don't work.
Perhaps theIf we decide that entirely blocking questions with spoilers is desirable, we don't need to push sites to do meta-tagging. The system could automatically filter from the HNQ any question that contains a spoiler block. That at least would be an automatic method; it relies on people using those spoiler blocks, but sites that care about spoilers are already have reasons to enforceenforcing that. I believe the HNQ already filters out questions containing certain words in their titles, so maybe adding this check is feasible.
Barring that, I recommend that you not click those questions, or that you use a userscript to filter your own HNQ list.
But, you might ask (as somebody did in a comment), what about questions with spoilers in their Three days after titlesThe Last Jedi came out, where "don't click/hover" isn't a solution? Spoilers in question titleswhat are either thoughtless or mean, and those sites already have rules about not doing that. Do you thinkthe odds that people who won't follow those rules would follow a different rule designed to keep those questions out of HNQ? Users should definitely be careful about how they post their questions, but not just for an HNQ filter — they should doabout it for the people on theirdidn't site too. If you're concerned aboutcontain spoilers in titles not being addressed by these sites promptly, your only safe option is to filter your own HNQ list.after all?
