I'd like to see a new default theme which has an options screen that allows end-users to easily reformat the basic layout. Choose how many sidebars, sidebar placement, allow them to easily change color schemes, and/or upload a header image. A selection of different font-stacks to choose from might be cool, too.

Kubrick was great when it first came out (particularly compared to Classic) -- it was clean and well-structured. But so many people just never changed it, that it practically became a joke. Building in some variation would be one way to add some freshness.