Better media handling: Make it easier to add images, Flash, Flex, and so on to websites built with Drupal.

Custom content types in core: Integrate portions of the CCK module into core to allow site administrators to apply this functionality more easily.

WYSIWYG editor: Incorporate a What You See Is What You Get HTML editor into core, so editors can add formatted text to their sites more easily.

Better performance and scalability: Make sites built on Drupal leaner and faster to load, improve performance for users that are logged into the site, and make it easier for Drupal to be used on sites that get lots of traffic.

Better tools to structure/organize content: Make it easier to create a meaningful site structure to hold all content in a way that makes sense for both administrators and visitors.

Basic Views-like module: Incorporate portions of the Views module to make it easier for site administrators to present site content in different, interesting ways to visitors.

Automatic upgrade functionality: Allow site administrators to download and install updates to Drupal, contributed modules, and contributed themes without needing to download and unpack tarballs and then manually deploy them to a site, making Drupal as easy to upgrade as your operating system.

Improved node access system: Improve control and permissions for who can access which nodes and what they can do to each node.

Better internal APIs: Make it easier to maintain Drupal and add custom modules for site-specific functionality.

Better external APIs: Make it easier to import data into a site and export data from a site. Improve functionality allowing administrators to consume and expose web services.

Usability: Reduce the learning curve for new users and make common tasks faster and easier to get to for experienced users.