In Civicrm 5.4 and in current version in WP Sandbox, it seems that the 'Developer' tab is no longer shown. What is the replacement/suggested method for adding a column to reports now?
To view developer tab for the report the user will need 'CiviReport: view report sql' permission. This is new permission added in recent version of CiviCRM for broader access control.
You can set permission by navigating to CiviCRM >> Administer >> Users and Permissions >> Permissions (Access Control) >> WordPress Access Control