Dropbox may come through for you in the end. They've got a feature called "Smart Sync" that is a network file system implemented as a kernel driver. See https:/

Dropbox may come through for you in the end. They've got a feature called "Smart Sync" that is a network file system implemented as a kernel driver. See https://www.dropbox.com/smartsync https://www.dropbox.com/smartsync and https://www.dropbox.com/help/desktop-web/filesystem-integration https://www.dropbox.com/help/desktop-web/filesystem-integrat.... Not sure if it's doing block level diff or not though.