Since a few days it is possible to download the new SQL Developer 4.2 in the Early Adopter Edition.

Infos about the new features can be found here by ORACLE or by ThatJeffSmith.

Here the list of new features coming from ORACLE:

• In-Line Editing: simply arrow around your currrent statement or script without needing to invoke an external editor
• Automatic Formatting: SQL output can be formatted to fit your screen or to CSV, JSON, Delimited, HTML, Insert statements, or XML
• New Commands: DDL, CTAS, REPEAT, INFO (an updated version of DESC), and many more. Use the HELP command for a full list.
• Client-Side Scripting: Use JavaScript in combination with SQL and PL/SQL
• SQL History: Records previous 100 executed statements and scripts and can be recalled with up and down arrow keys
• Tab Completion: Get assitance with object names, keywords, and more with the TAB key
• Oracle Database Exadata Express Cloud Service support
• New command, SET ENCODING. Example, SET ENCODING UTF-8, allows for reading a file for a certain encoding
• SSHTUNNEL now allows user to change default SSH port 22. Example, username@hotname:port
• INFO and CTAS commands now support TAB completion for object names.
• SET WALLET no longer requires a password for the wallet.