The intent is to keep Patient.gender to enable existing systems to use it until everyone is using SFCU or GI.    When using Patient.gender, it is important to consider how it will be used.  If you intend to use it for clinical care or any other use case, you must directly pre-coordinate with your trading partners to make sure you have a shared understanding of the semantics of the value in Patient.gender, as the FHIR specification DOES NOT identify any sort of precise semantics for that element.