WordPress 3.9 is due next month with extra features. But the good news is that the beta version is released today. I would like to put the points that have been taken care of in this release.
Point 1. TinyMice, the visual editor has been updated to the latest version. The new and latest version allows the developers to paste in the text block easily. The developers can also enjoy cleaner markup.
Point2. Widget management has been upgraded –the customizer. Now testing for adding, editing and rearranging is available.
Point3. Theme installer experience has been improvised.
Point4. Drag and drop feature for image editor is now available for developers. This is the most sought after features.
Point 5. Latest audio/video playlists. You can now upload a few audio or video files to test these.
These are some of the points that have been implemented or upgraded to the beta release. More information will be disseminated to you guys as soon as the main build is released.
Developers can now test their themes using the beta release. If you find or figure out any bug, do let the WordPress community know about.