That is an interesting idea - specially when you are trying to put out a nice and polished toot (a Blog announcement, a promotion message of some kind, etc).
I would suggest the title could be a more clear is this was called something like "Feature Request : Save as a Draft"
At first reading, I assumed the "Draft" in the header meant this was a preliminary version of your suggestion. I think this would be a useful feature.
I did not include Eugen in this reply, as he probably already has too many notifications at the moment. Let's see how people react and the comments. 😃