I'm trying to put together a skin framework from my experiences in the past, taking the good side of various wp&joomla frameworks.

Simply, what do you want your skin to do ?

From simple things like "i want to upload/change my logo", "mobile version".

To wilder ones like "it should have built-in, single-click gallery created from from folder", "ability to add scripts, js/css compression", "social integration (built in facebook/twitter plugin/widgets) etc.