Importing of duplicates - smarter detection and ability to ignore suggestions.
Ability to generate Smart Previews or 1:1 Previews for quickly flicking through library. Flicking through CC seems slower. For me, CC usually displays a quite blocky & low-resolution preview for a few moments before loading the full image.
Sharing to other social media outlets - Google Photos, Instagram, Flickr, 500px etc.
Right click on a photo and 'Show in Finder' (mac) to find the original photo (if stored locally is checked in prefs)
A counter for how many photos are selected - very handy. This could be displayed in the info panel when hitting 'i'. It currently just says 'multiple'.
When importing to an album, the ability to sort the list would be nice. Most often, I'd like it in reverse chronological order.
Facial detection and tagging - perfect task for Sensei
Smart geo tagging like Google Photos - somehow works out where photos were taken based on landmarks.
Both CC and Classic need the ability to search for and help clean up duplicates in your library.