Separating skins from core MediaWiki/Progress

I'm going to try keeping some kind of a progress log for the Separating skins from core MediaWiki project here.

2014-05-20

 * Asked "What should be the recommended / supported way to do skins? (A proposal.)" on wikitech-l: http://lists.wikimedia.org/pipermail/wikitech-l/2014-May/076591.html
 * Commented on pending changes aiming to move some skins out of core