The main point seems to be the introduction of additional dynamics through roles which are loosely coupled to a person. If they were coupled tightly to a person, a bunch of roles would form a traditional job description.
Isn’t there an inherent risk, that instead of a hierarchy of positions, you end up with a hierarchy of roles? That would just raise the complexity of the overall system, since there are — I assume—much more roles than positions. Therefore the number of (required) interactions within the system raises exponentially.