I'm assuming the obsVariant.component.ref-seq-assembly and molecularSequence.referenceSeq.genombuild should both be codeableconcepts. The obsVariant component is, but the genomeBuild is not. If not please, explain why there's a difference between how genomebuild/ref-seq-assembly values are shared across these two closely related resources.

@Kevin Power suggested getting this resolved and adding this tracker item.

See http://build.fhir.org/ig/HL7/genomics-reporting/obs-gen-finding-definitions.html#Observation.component:ref-sequence-assembly

The ref-sequence-assembly component is defined at the obsGenFinding profile super class level - not obsVariant.