1. The CO-AUTHORS plugin, which does what it says. One specific post or page can be assigned two or more co-author(s) by the blog editor. Very interesting. (I don’t get why the plugin developer forbids the co-authors to “edit” the post/page, though. Mystery, which I will try to clear up with the software architect of this plugin.)
2. The ROLE MANAGER plugin (not listed in the official WordPress plugin directory), which changes the standard WordPress matrix of roles and capabilities. It can redefine the capabilities of one category of users (i.e., one “role”), and can change the capabilities of one individual, but won’t assign common capabilities on a post/page-by-post/page basis (unlike the CO-AUTHORS plugin). To put it in another way, the ROLE MANAGER plugin can be used to extend (or restrict) the capabilities of the blog authors. Right now, they can only publish a post, not a page. In this instance, they would be allowed to write and edit pages —without the need for the blog administrator to promote these authors as full editors (which would be tricky since those multiple editors could then edit their peers’ posts –not acceptable in a big group blog with 71 blog posters).

Very interesting.

On Midas Oracle, one could have:

• Authors Mike Giberson and Adam Siegel writing together a post on “How Great An Exchange Inkling Markets Is“.
• Authors Chris Masse, Mike Giberson, David Pennock and Jason Ruspini writing together a page on “The Ultimate Prediction Market Definition“.
• Etc., etc., etc.
• If plenty of co-authors collaborate on a post/page, then my hope is that Midas Oracle could become more than just a “blog”, and be also a vertical encyclopedia on prediction markets. (Of course, participation inequality remains an issue.)

[External Reading: For the life of you, don't miss this blog post by Tim O'Reilly on Wikipedia.]

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UPDATE: The creator of the CO-AUTHORS plugin writes back to me:

Not allowing all of the co-authors the ability to edit a page is not by design; I just have to do more research on WordPress permissions to find out how to do so, if even it is possible.

I wonder whether using the two plugins together is the solution…

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UPDATE: My current thought is to give each Midas Oracle author the capability to create, write up and edit his/her own page(s). And then to assign co-authors to some post(s) and page(s), on a case-by-case basis.