We are going to publish soon new plugin which has a goal to simplify email templates management. It includes admin area where user is able to create and manage email subject/body (both html and text versions) and them system-wide constant values are generated for each email template and its elements, e.g. MYTEMPLATE_SUBJECT and MYTEMPLATE_BODY. This way emails can be easily added to mass mailer layers like swift mailer or so.
The other cool feature of this plugin is an ability to create and manage tags for email templates. So that user may define template with using of %NAME%, %DATE%, etc tags and they will be replaced with real values on the sending stage.
So it’s coming soon and let me know if you are interested in it or maybe have some good ideas or proposals.