The functionality that allows inbound Workflow Assignments to another User is a very good start. I'd like to see this taken to the next level to have the ability to set Delegates based on a Role and/or a Context. The practical default is essentially to "Delegate Up" or to an Administrative function that can determine who an appropriate alternate for a Use is based on the Role or Context of the Assignment.
Essentially it would be a hierarchy of delegates...
Default Delegate = Admin
Role 1 Delegate = User A
Role 2 Delegate = User B
Context X Delegate = User M
This would support the practical reality of people taking on different Roles in different Projects or Products (as is supported by the concept of Context Teams).