I'd love to see a major release dedicated solely to improving the UI and UX of the WordPress dashboard.

Menu items such as "Reading" and "Writing" probably don't make sense to the average user.

I also think a huge issue with the UX has to do with plugins. It would be awesome to see guidelines set for plugin developers that set some kind of standard for how a plugin should integrate with WordPress.

I spent 10 minutes the other day trying to figure out where the "Theme Checker" plugin installed - only to find it tucked away under the "Appearance" tab. While this makes sense after finding it, the initial hunt was not fun and I imagine it would be even more frustrating to a user unfamiliar with WordPress.