Raise your hand if you ever worried CMS will run out of National Provider Identifier (NPI) numbers? Anyone, anyone? CMS says in this recent FAQ you can set your worries aside:
The format of the National Provider Identifier (NPI) and the assignment strategy will enable the enumeration of over 200 million health care providers. At the current rate of increase in the number of providers in the United States, this should enable the Department of Health and Human Services to enumerate health care providers for 200 years.