Having the ability to create your own template pieces that can be used to generate a new template would be amazing. For example, if you have 3 headers you use for all your templates, you could create all 3 and have them as ready to go options in your builder under the 'Headers' section.
We implemented Saved Sections on our new builder on PoliteMail Online. I'd love to hear from our customers if this covers what you were looking for.
Thank you for your idea. We will share it with the Development Team.