Maybe an upcoming step is to hike up the Centurion card fees even higher, let that drive up churn of the customer base, and even perhaps shrink the customer base to an even less-value-focused subset of current and prospective Centurion card holders?
Even obsolescence of the product isn't out of the question were Amex's cost to keep a specialized product to exceed the value of the halo effects of the product. A decline in service levels may be one way to get closer to making a product obsolete -- whether by design or by neglect.