It would be a really powerful feature that users would be able to assign a url to the folder (something short like folder123.sync.to), which leads to a web drive of the folder when at least one of the folder's devices are online.
The initial handshake is handled by the node, but file transfers are direct from the web device to all the normal devices. This would enable users to upload or download files from their synced folders on a device without Sync installed.
I foresee this would require extra framework for the nodes, so this might work as a pro-only feature.