There's a column called
customer_address_entity. Is this used for anything?
Magento gives you the option to generate Human Friendly IDs for customer accounts. It's disabled by default. If you want to enable this feature, you can go to:
Stores > Configuration > Customers > Customers Configuration > Create New Account Options and set
Generate Human-Friendly Customer ID to
Yes. That will generate Increment IDs for customer accounts.
Just an addition to the answer by the original author:
The increment_id serves no purpose at the moment, but can easily be transformed to a working one (although I see no business case for this).
In the column
eav_entity_type, just add an increment_model for the entity
customer_address. Then add an observer for
customer_address_save_before and call that model to generate a new increment_id.