Just thought how handy it would be to have a cloud based storage system which treats your device's local storage as an automatically-maintained cache. A bit like Dropbox only instead of choosing desktop (clones cached locally) vs. mobile (no local storage), the filesystem automatically decides for you, flushing old copies you haven't touched in a while and downloading stuff you are revisiting.
All you see is that you just format and mount your storage device or partition using the magic FS and its capacity magically extends into the cloud, just cacheing locally what you are most likely to want in a hurry or when offline.
Whatever client device you have going, you format and mount its local storage as the "same" pile of stuff and it then manages that local cache according to local needs.
At a pinch it could even pass your swap file out to the cloud, giving you a rude message about running 500 apps on a Sinclair calculator but at least not losing anything.
Does such a thing already exist?
The eternal help vampire