I'd love to get up something like http://whatcanidoformozilla.org but for Wikimedia.
The decision tree will be stored as some plain text format and I'll enable a way of foundation/community members to edit the content of it. (whatcanidoformozilla.org does this by enabling contributions via github).
Another option would be creating a page similar to https://www.mozilla.org/en-US/contribute/ which is also awesomely friendly and encouraging, and if you go "Get involved" it asks a couple of questions and then it actually sends the information to a human, so that you get real interaction and advice for engaging (and a first contact!).
Will define more as Wikimania comes along.
* Links for (potential) content/categories
* https://www.mediawiki.org/wiki/How_to_contribute
* https://www.mediawiki.org/wiki/Annoying_little_bugs