I would post this reply in your thread at Wikipedia Review, but I refuse to post there, and removed almost anything I ever created rather than give content to some of the Wikimoles that continue to infiltrate the forum even after I salvaged it from the take-down attempt by that British cop. But here’s the deal, in response to your question and statement: “If you wanted to start a free-to-use, authoritative encyclopedia then what software infrastructure would you use? The rise of Wikipedia derived largely from the accessibility of the software.”

Would you be so kind as to post the following extremely accurate and very useful reply to your question that was otherwise ignored in the thread where you asked the question, and attribute it to a person who refuses to post at the forum because too many wikipedia sympathizers hang out there?
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MediaWiki can easily be modified to accomodate expert moderation. Not only can MediaWiki be modified to allow rational, mature, professional moderation, it already has been so modified. The fork is at http://sourceforge.net/projects/groupwiki

For the site administrator who wants a more simple solution than a entire fork, a MediaWiki installation can be modified with a simple extension — Group Based Access Control Extension http://www.mediawiki.org/wiki/Group_Based_Access_Control_Extension

The extension and GroupWiki can be used in tandem for further granularity. A good page layout for revised MediaWiki installations that allow rational control of access for group editing can involve some changes to edit tab algorithms too, but how hard is that? Changing a few lines in skintemplate.php is all that takes.