It occured to me this would make an excellent O'Reilly/Wikibook and kill two birds with one stone.
"Learning PHP by example, with MediaWiki"
You get the book, and a cover disk with a snapshot of the mediawiki software. It could be a "live" bootable cd, with everything setup and running - or just a specific version of the code.
Then, run through the basics of PHP pointing people at specific pages/code in mediawiki as an example.
The reader would learn about PHP, and get a fully functioning advanced wiki for their own use. Plus the knowledge to tweak it to their needs.
Wikipedia would gain exposure, and if it was published, possibly some revenue to fund other work. Plus an easy way for developers to get involved.
Sadly my PHP skills are rubbish, and I too don't have the time, so just throwing in a suggestion. Another take on the same theme would be if someone like O'Reilly were to be interested, they might fund an estalished/star PHP hacker to write the book - which would for a brief window bring in some top-rated skills specifically focused on making the code easier/cleaner (not that I'm suggesting it ain't already ...).