I think we’re already there but not in the way OP describes. People haven’t had great experiences with Chrimebooks and storage is cheap

Think of your Google drive, OneDrive or Apple drive. The most common scenario is you use local storage for reliability and responsiveness, but it’s always aynching to the cloud. Many of your files may not even exist in local storage but it looks like it does

Or consider Apples approach to photo storage. You can choose to use iCloud for photo storage and it keeps only a thumbnail on local storage. Your basic browse and search operations are reliable and responsive, and but you download the full photo as you need it