Presently, Patient.gender is a CodeableConcept. I believe that this is a wrong assessment of complexity- yes, there are multiple coding systems for gender, and yes, a few institutions use an extended list of codes (i've even seen 17). However 99%+ of systems use Male, Female, Other, Unknown, and all the additional codes are finer grained variations of these.

It would be a lot simpler to fix patient.gender to a simple code (M,F,O,U), and define an extension for the few systems that want to exchange a finer grained gender than that. This has the same functional outcome, but makes it much easier for implementers, who know that they'll get one of the 4 base codes at least.