http://www.w3.org/2009/cheatsheet/#search,cite says:

"The cite element represents the cited title of a work; for example, the title of a book mentioned within the main text flow of a document."

This reflects what the HTML5 spec was saying in early 2013 (the "CHANGED" notice <http://www.w3.org/TR/html-markup/cite.html> is undated, but another of your pages suggested it dates 28 May 2013, though I see some evidence like this <https://www.w3.org/Bugs/Public/show_bug.cgi?id=10998> that the "titles-only" epxeriment dates back to ca. 2010-2011 at least). However, this excessively restrictive model was abandoned by late 2013 (as reported, e.g., at: <http://html5doctor.com/cite-and-blockquote-reloaded/>).

The current, non-draft version of HTML5 (28 October 2014) is quite clear that the element may include any citation data as along an an author, and/or title, and/or URL are present (including in abbreviated form); see in particular "4.5.6 The cite element" <http://www.w3.org/TR/html5/text-level-semantics.html#the-cite-element>: "It must include the title of the work or the name of the author (person, people or organization) or an URL reference, which may be in an abbreviated form as per the conventions used for the addition of citation metadata". Note in particular that it says "include" not "consist solely of"; it's perfectly valid for an entire standard reference citation, as used in a journal paper's footnotes, to be marked up with <cite>.

See also "4.4.4 The blockquote element" <http://www.w3.org/TR/html5/grouping-content.html#the-blockquote-element>, in which it is noted that it is now permissible to use <cite> inside or outside <blockquote>, though I'm not sure if the Cheatsheet material on <cite> needs to address that.

All the usual suspects, like HTML5Doctor, agree on how to interpret it, except:
1. your own 2009 Cheatsheet database (which seems to include info up to 2013 actually), and (as a direct consequence of what the Cheatsheet says)
2. WHATWG's "Living Standard" <https://html.spec.whatwg.org/multipage/semantics.html#the-cite-element>.

I've written to WHATWG to change it, but they're citing the W3C 2009 Cheatsheet, instead of the 28 October 2014 actual standard! (This despite the fact that plenty of WHATWG people know this has changed, as evidenced by the material here: <https://wiki.whatwg.org/wiki/Cite_element>.)

Regardless, I think we all know now that people use this element for whatever citation data they feel like, since that's what it was used for in HTML 4 <http://www.w3.org/TR/html4/struct/text.html#h-9.2.1>, and that's what it's used for in current, modern, official HTML5 (already cited), AND it's also what HTML5.1 Nightly is doing, too <http://www.w3.org/html/wg/drafts/html/master/single-page.html#the-cite-element>.

The entire notion of limiting it strictly to the title of the work was not viable, but W3C not updating its own materials is causing real-world implementation problems.  For example, Wikipedia is avoiding almost all use of this element until this mess is sorted out; the conflict between W3C's spec and WHATWG's take what the element means are causing enough cognitive dissonance no one at WP wants to touch it. (This particular dispute is what brought me here, since I'm trying to get our [WP's] citation templates to wrap in <cite> instead of <span>.

PS: The recommendation to forcibly italicize this by default, found in various places including WHATWG's documents, is particularly unworkable, and did not make sense even for title-only usage. No style guide in the world I'm aware of (and I have quite a collection of them) advises italicizing all titles of all works, but only titles of major works: books, magazines, journals, feature films, plays, operas, albums, TV series, comic book series, etc.; titles of minor works (chapters, articles, short stories, poems, short films, skits, operettas, songs, TV episodes, comic book issues, etc.) go in quotation marks without italics.  This element should have no particular style imposed on it, especially since probably its widest actual deployment is marking up the usernames of blogs and forum posters on their original posts and when quoted by others.

PS: There's a typo at <http://www.w3.org/TR/html5/text-level-semantics.html#the-cite-element>; it actually reads "author(person, people or organization)" (missing space after "author"). This error is repeated at the HTML5.1 Nightly draft <http://www.w3.org/html/wg/drafts/html/master/single-page.html#the-cite-element>.