It is a very common scenario that a user will build a page and then decide that all future pages should be based upon it. It would be very helpful if there was an easy way to save a page as a template. The template editor would then let the user parameterize the template as necessary, but the basic editing would be the same.
If page templates were actually stored as specially marked pages then this would be even more straightforward. A nice benefit of this would be that you could specify labels and permissions on your page template that would then apply to pages created from it.