Techincally NOX is not requirement for lean, but my understanding is that MSD software requires it. According to Bimmerprofs: "if engine control unit memory contains error messages, which refers to NOx catalytic converter and/or NOx sensor, most advanced modes – Stratified charge and Homogeneous lean – won’t be available. The engine will run in alternative (emergency) operation mode: Homogeneous injection."
and "In no way, the N43/N53 series engine can work without NOx system."
And this is what they say about NOX map-out:
https://bimmerprofs.com/disprogramming-nox-system/