The spec currently defines consumer mutability of an attribute in the attribute type definition. Questions have been raised about whether that is appropriate. Few scenarios that complicate this:
1) Collection type 'items' attribute may be mutable or not depending on the kind of collection.
2) the consumer mutability of an attribute may depend on an instance not the type. Moving this to the type necessitates unnecessary invention of additional types
3) the mutability of an attribute may depend on other factors such as authorization/credentials of the consumer or it may change with time (because changing the attribute value may make something else inconsistent).
Issues 180, 196, and 199 depend on resolution of this issue.