I was on KuCoin and accidentally sent BTC to the BCH address (thinking I was buying BCH). Of course nothing shows in the BCH wallet on KuCoin. I can see it on the blackchain but cannot access it.
At a technical level, this is possible. You can retrieve BTC from a BCH address by importing the private key into a BCH wallet.
However, for many exchanges, security systems do not allow the removal of private keys (for instance, they may be locked in an HSM, or tied down through other security controls). They would also not allow for the signing of arbitrary transactions in some cases, preventing manual recovery.
Your only option is to reach out to Kraken and request them to access the private keys in some manner and sign a transaction for you that sends the BTC back to an address you control. It may not be possible with their setup, but it is your best (and only) course of action.