Add line duplication to Xcode key bindings located at /Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Versions/A/Resources/

IDETextKeyBindingSet.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  
    <!-- Lots of code already there -->
  
    <!-- Add the following key and dict after installing or updating Xcode -->
    <key>Duplication</key>
    <dict>
        <key>Duplicate Line</key>
        <string>moveToBeginningOfLine:, deleteToEndOfLine:, yank:, insertNewline:, moveToBeginningOfLine:, yank:</string>
        <key>Duplicate Lines</key>
        <string>selectLine:, copy:, moveToEndOfLine:, insertNewline:, paste:, deleteBackward:</string>
    </dict>
</dict>
</plist>