Option to save email you're working on as a template.

Often when working in an email, you build one the way you want it from a template and then wish that you could save that email as a new template.  The option isn't there—you'd have to get out of that email, go into the design tab, then build a new template (recreating that whole email again). 

It would be really nice to just have an option to save the email you're working on as a template right there from the email. 
The go-around is just clone the email, but it's not as handy as having a template ready.