A sftp special remote would be nice because gpg operations could be
pipelined to the network transfer, not requiring the creation of a full
file to disk with gpg before the network transmission, as it happens with
the rsync special remote.

There should be some libraries that can handle the sftp connections and
transfers. I read that even curl has support for that.

> Another reason to build this is that sftp has a `SFTP_FXP_STAT`
> that can get disk free space information. "echo df | sftp user@host"
> exposes this, when available. Some sftp servers can be locked down
> so that the user can't run git-annex on them, so that could be the only
> way to get diskreserve working for such a remote. --[[Joey]]
