The search parameters for StructureDefinition show the following

valueset reference A vocabulary binding reference StructureDefinition.snapshot.element.binding.valueSet

However, there are at least two problems:

1. I don't see how you can have a reference to an implicit ValueSet, so yuo cannot search for StructureDefinitions that use them, and

2. the type of StructureDefinition.snapshot.element.binding.valueSet is uri or canonical

The type of this search parameter should be changed to align with uri and canonical.