It's totally unrelated but something I would really like to have right now would be a header with the average connection bandwidth (or just thresholds). This could be really useful to reduce the amount of data sent if the connection is really bad.
It's not useless, since it allows the site to avoid being blocked by hiding the "bad" content. Ideally blockers would be smart enough to recognize and block only the "bad" DOM elements, but they usually just block the whole page, if not the whole site.
Given that, I see these possible outcomes
- the client's admin might not care about this site at all (effort to hide stuff would be wasted?)
- the client's admin might consider content 'unsafe' that seems fine/okay to the site operator => Blocklist, failed to archive what you suggest
- the client's admin might consider content 'safe' that the site now refuses to share => Curse site and Mozilla, switch browsers and/or consider that site broken and the operators morons (similar to 'breaks zoom on mobile devices' today, for example)
http://en.wikipedia.org/wiki/Motion_picture_rating_system
However, this got me thinking that across cultural lines there are a lot of shades to what is "safe". So a website based in Austria might want to restrict different content than a website based in Australia, and who knows where the "browser" is based.
Of course your comments about the site actually implementing anything/correctly still apply.
That said, I think the implementation should have an admin-controlled site whitelist and even a way to disable the header even if parental controls are enabled, to prevent (3).