Since this executes the RPC server for each private key though, it's going to slow down once you reach a hundred PKs or so, especially if your node is somewhere far away n the public internet (then latency also has to be considered).
I'd make sure I connect to my Bitcoin server via a secure transfer protocol, because there's sensitive info transferred.
The only option would be calling it via an .onion address on Tor, since even the RPC password is sent unencrypted. It is indeed unsafe to issue any RPC call with plain HTTP because of the unencrypted password.