Add more fields to Action Rules -> Send Email action templates

I've found I can accomplish most of what I need to do in Setup -> Processes -> Action Rules using the Actions panel "Send Email" action, but that action is missing a very key variable - the Request Description. Here's what's available in my instance (v. 12.0.1):

http://note.io/1asPuTZ

Ideally, one could configure any attribute that's stored in the database to be added, but all I really need for now is Request Description to make this more useful.

If you are only statically adding additional fields, may I also request <ticket_url> as well, since I'm currently having to form it via string concatenation with <ticket_id> and a hard-coded URL string.