I finally got around to organizing my Skinning system page and cleaning out the ideas sitting there that I actually dropped or replaced. https://www.mediawiki.org/wiki/User:Dantman/Skinning_system
Some notable things: - A template system is planned. The idea is slowly stabilizing. - I plan to replace things like bodytext, newtalk, sitenotice, catlinks, dataAfterContent, etc... with a 'regions' system that lets skins define their own areas with certain parameters, extensions define things they want in certain types of areas, and MediaWiki figures out what to put where. - I have an idea on how to eliminate content_{actions,navigation}, personal_urls, toolbox, language_urls, etc... in favour of a more flexible system: https://www.mediawiki.org/wiki/User:Dantman/Skinning_system/Link_lists_rewri... - I've dropped the idea of controlling the SEARCH/LANGUAGES/TOOLBOX from the navigation editing interface and perhaps even the skins defining the navigation blocks themselves. Instead I'm thinking of users being able to define navigation blocks of different types. Drop those in for use in different skins. And the sidebar would become a widgetized sidebar setup where from a separate interface you can drop navigation lists as widgets into the sidebar, alongside the default search/etc..., raw blocks of wikitext, and extensions will be able to implement alternative widgets like donation buttons, advertisement blocks, etc... also extensions may be able to implement context-sensitive types of navigation that can be dropped in. eg: To make something like what Blender's Wiki tried to do possible.
An example of a possible way the Vector skin might be built with this system: https://gist.github.com/1239039