Uh, I did. Right there in the first sentence: "Web Upd8 has the latest LibreOffice UI mockups...." And it's also in the subject line. 
-zridling
Mockups can be official and unofficial. If the mockups come from the official team it means that the proposed designs could very well make into the actual product. Any other mockups by independent designers are unofficial. They are unlikely to find their way into the final product, unless the product developers embraces it, in which case, it becomes the official mockup.

Not really.
These mockups have some great ideas. And Libre is very open to suggestions.
So until somebody at Libre says this particular concept is a complete crock and won't be considered, it remains part of the meme surrounding LibreOffice. And being an open software project, there's also nothing to stop the implementation that interface as a side project even if the Document Foundation's LibreOffice programming team decides to ignore it. (I say ignore because you can bet somebody has already brought it to their attention.)
There's even a page on their website specifically for UX and Visual designers. Link here.
Note: DevArt is consulted for design ideas and inspiration a lot more often than most people realize - so don't rule something out just because it's found there. I've seen many interface concepts displayed on DeviantArt that mysteriously appear in software products later on.
I agree what you say, but my initial argument still holds - that they are not official, so don't pin your hopes on THIS particular design. And just like you said, there could be and IS dozens of Liberoffice designs floating around the web, any of which (or none) could becomes the actual UI.
I just want to say that if you don't label a mockup as unofficial, people assume they come from the developer.