Slicing is a nice idea for defining complex or composite data elements used by several FHIR ressources.
"Within a structure definition, a slice is defined using multiple element entries that share a path but have distinct names. These entries together form a "slice group" with useful featured described in http://www.hl7.org/fhir/2015May/profiling.html.
However in the FHIR ressource "DataElement" itself the use of slicing within the ElementDefinition ist not allowed: see https://www.hl7.org/fhir/dataelement.html
=> Definition of element, No base allowed, No slicing allowed
What is the reason for not allowing slicing within DataElements?
The purpose of DataElement is to define elements. All data elements defined are stand-alone - they don't inherit from other data elements. As such, there seemed to be no place/utility for slicing. (It exists on DataElement from its use in StructureDefinition.) Do you have a use-case for slicing when defining DataElements?