You can use pigz with SSH as you can pipe commands over SSH (google it). If nc is faster than scp, I guess encryption is a factor, but then they're not comparable solutions to the same problem.
Sure you can :). Naturally transfers via SSH "suffer" from the encryption overhead but prevent MITM/network sniffing etc. The author points out that (only) in a trusted LAN you could use this solution to make things go faster.
I guess the title should be a little more mild - scp isn't going away, or rsync via SSH for that matter.