Currently, we have 3 parameters which can be used in the Notification email Subject:
Execution packages which are scheduled normally have the environment name in them,
but sometimes we need to manually run a more generic execution package in an environment... for instance, to force a full load. 
In that scenario, it would be helpful to be able to use the %ENVIRONMENT% project variable in the notification.
Our only alternative is to setup multiple copies of execution packages right now.