I'm a bit worried that, as far as I see, the Syncthing protocol doesn't really allow having servers/peers that don't see plain-text. (Since I think it mostly just uses TLS to keep things secret from eavesdroppers.) I've always been looking for an open source Dropbox-like that allows having storage that only sees ciphertext (despite the fact that it would require a little key management from the user, which I think is a usability challenge, but one that can be overcome).