In Sublime Text, it\'s easy to select the next instance of a word by pressing command + d and also place multiple cursors by pressing command & clicking
There's the Xcode-Multi-Edit-Plugin. It's still not quite like Sublime because the multiple cursors can't be used to edit beyond the selection you made when you started command-d-ing but it's close enough.
The plugin is not updated for Xcode 7.3 but this can be easily fixed by adding
ACA8656B-FEA8-4B6D-8E4A-93F4C95C362C
to the list of similar UUIDs in in the plugin's Info.plist. (Found at ~/Library/Application\ Support/Developer/Shared/Xcode/Plug-ins/XcodeMultiEdit.xcplugin/Contents/Info.plist)
Another promising plug-in which currently lacks Xcode 7.3 support is Multiplex.