Conflict of interest is a threat, not a control.

Explanation
Cryptographic keys should not be stored along with the data they secure, regardless of key length. We don't split crypto keys or generate redundant keys (doing so would violate the principle of secrecy necessary for keys to serve their purpose).

With multitenancy, eDiscovery becomes more complicated because the data collection involves extra steps to ensure that only those customers or systems that are within scope are turned over to the requesting authority.