I very much support Ori's proposal. We discussed it at length during the product retreat and I think we can easily avoid the pitfall Jarred is being cautious about by simply making a few configurable parameters for the skin default to one value, but be deployed on our sites using another.
This also gives us the ability to adjust the branding of the theme between sites. Again - this would be subtle, but we know that people get confused as to which site they are on when navigating between WP and Commons for instance.
Finally, these "configurations" could possibly later be adjusted by admins using a special page. Wordpress themes often allow key theme colors to be adjusted this way, and people actually do customize their themes quite often, further increasing the effective diversity of MediaWiki skins throughout the internet, helping to prevent our brand from being watered down as it to some degree today.