As documented in Windchill Help Center, Cascading rules are enabled for attributes which datatype is either "Boolean" or "String" with an enumerated value list constraint directly backed by a global enumeration.
However there are OOTB MBA's such as "Complexity" (on Change Notice) which are constrained by a legal value list and therefore they can't be used in Cascading rules.
Obvious workaround is to redefine IBA supporting same behavior but first, it requires additional effort on Workflow definition side (for the use case of change notice refered above) and layouts definition side as well. And secondly, it would make sense that OOTB attributes are supported in cascading rules instead of customizing data model for that purpose only.
