Text fields for disclosures next to the article entry form in the CMS and a <p class="disclosure">-tag will do just fine, thank you. Plus you would still have to implement all that even if a <disclosure>-tag existed.
You're reading an article. It has a disclosure associated with it. Wouldn't you like to know that?
I mentioned the possibilities of the situation arising in other countries in the third sentence. It's only US-centric because the US (as far as I know) is the only one who has implemented such a policy. I think it's safe to assume the same will happen in other countries.
What’s so bad about something like
<p class="disclosure"><em>Disclosure:</em> XYZ</p>
Put it inside the <article>-tag (in our glorious HTML5 future) so you don’t lose it. A <disclosure>-tag just seems too specific.
But I do agree it seems a little too specific.