We are trying to include the Issue status in the Subject of the customer notification emails but the only available variable under templates for insert in the subject are : Issue.key, issue.summary and portal name.

Request status is however available to be inserted in the body of the email which we don't think is really as useful as having it in subject.  

When you are in the templates screen making modifications you can actually type in ${request.status} in the subject, send a test email and this will actually work - adding the request status to the subject of the email - but when go to save the changes it gives you an error: "Email subject contains an invalid variable - ${request.status}

 Update 2021-11-15

Please consider allowing all fields that can be found in documentation: Managing service project notifications - Jira Service Management Data Center and Server 4.20 - Atlassian Documentation