Microsoft had this feature built in windows 8 / 8.1 and removed it in Windows 10 cause it "confused" customers. Hope this will nudge them to bring it back.
It's removed in 10? That's kind of a disaster, as it's critical to making the Surface and various tablets usable.
It removed "placeholders" and added a selective Sync feature but its not the same. Placeholders experience felt more intuitive. Files that were only available online were marked so you know. I guess the problem started cause a lot of users would not be able to access files when offline and started complaining to their support service. Too bad though I loved that feature.