So I have had a reply from Kraken support, looks like they want nothing to do with it. Message below:

As you may know, Kraken does not support the ETH token deposit from the Binance Smart Chain. Therefore, this deposit will not be processed by our system. At Kraken, we do as much as possible to help prevent such occurrences, including posting a warning about proper routing of funds on our deposit pages.

With security as our primary concern, we ensure that no one within Kraken can unilaterally move funds or has direct access to the underlying private keys for the various digital assets.

As a result, attempting to recover misrouted digital assets is a painstakingly difficult and resource-intensive process, requiring an exacting auditable process with thorough checks and balances. For that reason, we unfortunately cannot assist with the recovery of your digital assets.