There's no way to get a struct type property value from a type descriptor

[jackfirth]

This is mainly a problem for properties that associate a value only with a type, not with each instance. For example, consider a prop:default-instance property and a (default-instance type) function. This function should accept something like a struct type, not a particular instance. For rebellion/type, this means that struct type properties should be accessible via an initialized type descriptor.