Comments
Some resources have nullifiers and some do not, and there is no rationale why some do and some don't. For example, an Observation can be "entered in error" but a MedicationStatement cannot, a MedicationPrescription can, but a Immunization cannot, and so on. Either all resources should allow for a nullifying attribute, or none should. If the former, there should be a standard attribute to indicate nullification of the resource. The existence of a standard nullification element across all resources will greatly simplify search and processing. This is just one more example of the willy-nilly nature of resource definitions.

Grahame's Comments
Presently, committees add these if they make sense in the domain. For many resources, a concept like this doesn't make sense. And so I would be against adding this to every resource. It would make some things more complicated. But perhaps, if we have a list of ones where this does apply, then we could look for patterns; it would be possible to define another abstract "nullifiable' resource, for instance. The details would should whether this is a good idea or not