Why
The ability to store files in the cloud greatly increases the reliability and availability of data.
Imagine that you are going abroad. You take a synchronized laptop and phone with you, but you are not sure that the Wi-Fi in the hotel will work, that the mobile network will work, and even that there will be sufficient access to electricity. You cannot predict how often you will be able to connect your laptop and phone to the network at the same time.
At the moment, the best solution would be to use Dropbox instead of Syncthing — Dropbox will be predictably online when you connect at least one gadget. But it would be great if Syncthing could be relied on in these cases as well.
How
This can be implemented if, in addition to Devices and Folders, we add a third entity, say Folder-in-Cloud.
Folder-in-Cloud can be set up by providing credentials required by a cloud storage (Storj, Dropbox, so on), and pointing the path in the remote storage. For example, we could configure Folder-in-Cloud named “MyDocs in Storj”, which refers to particular path in particular Storj bucket.
Folder-in-Cloud is not a Device, because it is passive by its nature. It can be read or written from a local Syncthing instance via cloud API. But the cloud does not run any specific Syncthing software, and even not aware that it is used by Syncthing.
Folder-in-Cloud is not a local Folder, because we never have direct access to it. It is always something remotely accessible, but never here.
To use Folder-in-Cloud we turn on synchronization between our Folder “MyDocs” and Folder-in-Cloud “MyDocs in Storj”. So our real filesystem folder on particular host gets two-way sync with the cloud. It is done by local Syncthing instance. This does not directly affect other devices.
The Folder-in-Cloud may be displayed next to Devices list in particular Folder settings. We can sync Folder to other Devices and/or to other Folders-in-Clouds.
Probably each Folder-in-Cloud should be compatible only with on id of ordinary Folder. So we can sync “MyDocs in Storj” with “MyDocs”, but not with “MyPictures”.
It would also be great, if after creating and configuring “MyDocs in Storj” on one Device, we could share this Folder-in-Cloud (i.e. configuration settings) with other Devices.