I just read a new article in the WordPress Blog that talks about improving plugins by using a changelog file. The WordPress team added a new feature to the plugin directory to allow developers to include a changelog with their project. The changelog informs us what changes have been made in each version of the plugin, so that the user can make a decision about when to upgrade. It would be a very good idea to add this feature to the Theme Directory too.
Many WordPress Themes include a changelog in the readme.txt file, however it is always easier for the theme users to access this information directly when they browse for new WordPress templates. I hope they can implement this feature in the Theme Directory. As for the Plugin Directory, the changelog information is displayed as a separate tab and also in the dashboard of your WordPress blog when you view the details on a new version of a plugin. Click the link below for more information about this topic.