Organice does support Google Drive, Dropbox and WebDAV. (Organice is a fork of org-web)
More fundamentally, if you (anyone reading) can think of any easily usable way to sync files between devices, I think it might not be too hard to get Organice/etc. to support that as yet another backend.
More fundamentally, if you (anyone reading) can think of any easily usable way to sync files between devices, I think it might not be too hard to get Organice/etc. to support that as yet another backend.