|This essay contains the advice or opinions of one or more Wikipedia contributors. Essays may represent widespread norms or minority viewpoints. Consider these views with discretion. Essays are not Wikipedia policies or guidelines.|
Unsolicited redesigns of popular websites are extremely common, especially as student projects or tools to fill out a design portfolio. As a top ten website, Wikipedia has been subject to this phenomenon many times. Since these are redesigns of a site that everyone uses, they often get picked up by blogs.
Why unsolicited redesigns are welcome 
- Radical change (or in this case, a proposal for a radical change) is strongly encouraged by one of Wikipedia's core guidelines: "If you see something that can be improved, improve it!"
- They let an individual or small group of designers flesh out a set of new ideas without constraints.
- They allow novel ideas to be thought out and visualized, even if they would be hard to implement immediately.
Even objectively bad redesigns may have the following positive outcomes:
- They start a conversation.
- They show a hunger for better design.
- They can provide inspiration for new things to try (or to avoid).
Why unsolicited redesigns can be problematic 
Independent of the merits or drawbacks of any individual design decision, the following are some fundamental problems present in any unsolicited resdesign:
- The purpose of an unsolicited redesign is often to showcase the talents and ideas of a design firm or designer, more than to improve the project in question.
- They rarely ask users what they want or need and often don't take into consideration the complex community issues that a site like Wikipedia has.
- Any serious redesign requires proper user testing.
- They rarely consider how hard a redesign would be to actually implement.
- They rarely consider past work: how the interface has evolved, or why certain design decisions were made.
- They often fail to appreciate that Wikimedia's websites are multilingual and global, rather than US-centric, English-only or even Latin-only.
- Even really great ideas may be rejected due to "Not invented here" syndrome.
- The copyright status of unsolicited redesigns is often unspecified: If so, one who use them makes a copyright violation. If your proposal is on a different website, please release it explicitly under a free license or into the public domain.
Amir Aharoni dissects one design highlighting several such problems.
But my redesign is a serious proposal! 
Wikipedia is an open community, and always needs good ideas. If you want to get heard, then get the word out in a few places, and choose a space on-wiki to discuss your ideas.
Here are some places to put serious and thought-out Wikipedia/MediaWiki redesign ideas:
English Wikipedia Main Pages and portals:
- The English Wikipedia has a 2012 main page redesign contest underway
- To discuss redesign ideas with editors, post to the Village Pump for Proposals
Other Wikipedia and sister project design (article and talk pages, mediawiki skins):
- See the Wikimedia Foundation global design page on mediawiki.org
- Post to a mailing list like Wikimedia-l
Unsolicited redesigns of Wikipedia 
Past unsolicited redesigns of Wikipedia include...
- http://ency.cl/opedia (blog post)
- Greplin Wikipedia Search Redesign Challenge (site no longer available)
- http://dribbble.com/wirwoluf/projects/104912-wikipedia-redesign (2013-01-18)