11
As it's mentioned on MSDN, user cannot customize status in The Opportunity entity.

Title : Add newly created custom fields to the Opportunity Close form
URL : https://docs.microsoft.com/en-us/dynamics365/sales-enterprise/customize-opportunity-close-experience#add-newly-created-custom-fields-to-the-opportunity-close-form

If user can add options to status in the Opportunity entity, that will make Dynamics 365 (Online) more flexible system to adapt their own operation.
STATUS DETAILS
New