With the increasing amount of Javascript code included in the default configuration of Commons I feel the need for a convenient configuration mechanism to enable and disable specific extensions and to set customizable parameters.
I created such a framework here: http://commons.wikimedia.org/wiki/MediaWiki:JSconfig.js
It allows the creation of parameters (with descriptions and default values). These parameters are used to dynamically generate a new Tab in on the MediaWiki Preferences page. The preferences on this page are saved as cookies (and automatically restored from the cookies).
Extensions can conveniently define a parameter set and query it without having to worry about a user interface to change them and a logic to store them.
It needs some further polishing to make the preferences page more structured, but I allready have some ideas. If this gets adopted I'll certainly put some more work into it.