Running the zcash client on an internet connected PC is a security vulnerability, because the private keys could be stolen from disk, or out of memory after being unencrypted, by malicious software that could get onto an internet active computer. This is likely the reason why nobody uses z-addresses for permanent storage.
I understand that sending z-address transactions from the limited compute power available on hardware wallets like Trezor or Ledger is not yet possible. However, it should be possible to setup two computers with the zcash client, one of which is connected to the internet but does not have your private key, and the other one offline which does not have your private key. In order to sign a z-address transaction, it should be possible to copy over certain data to the offline computer for signing, and then copy the result back to the internet enabled computer for sending over the internet. In this fashion, the offline computer would essentially be a hardware wallet.
Does anyone know how to do this?