Several customers now in the financial and legal industries have requested that they can preview an email template prior to distributing the campaign activity, primarily because the email mailshot must be approved before sending. Because the users who wish to preview/authorise the email aren't the users who actually distribute the campaign activity (i.e. senior partners & directors), they cannot quickly view the proposed email because the email template is only selected after pressing 'distribute campaign activity'.
Adding a relationship to the campaign activity to show a lookup to the 'proposed email template' is not possible either due to the email template not being customisable.

A quick win would be be to enable relationships to be added to the email template entity.
The slickest solution would be to have a preview window within the campaign activity so the user could see the email to be distributed and make amendements prior to distribution.