rowanblewett

There isn't a built in feature that can duplicate block layouts, but there is a way to do it! And to be honest, it literally saves me hours every day!
The solution is the PRO tool from Squarewebsites. It's a Chrome extension that adds a button to your Chrome browser's toolbar that gives you new almost magical capabilities! It was designed by Michael in Ukraine 🇺🇦.
For example, here's a section containing a block layout that I want to copy. As you'll see below, there's a text block and and an image block. I can copy this layout of blocks by clicking 'COPY':

 
Having copied the blocks, I can click 'INSERT' to insert this block layout into my new section on a new page:

 
There's also a PRESETS option. This allows you to save your favourite layouts (the ones you've designed) and then reuse them over and over again!
NOTE: This post was created before Squarespace introduced the new Squarespace 7.1 feature known as "Fluid Engine" in July 2022. The description and images in this post were created using "Layout Engine" (now referred to by Squarespace as the "Classic" editor), and whilst they still apply to sections created with the Classic editor (such as those on Squarespace 7.0), the tool does not allow duplication of Fluid Engine sections. 
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SQS 7.1 has a number of solid page templates, but I often create pages in a specific layout with sections and copy according to different needs, such as a lead page with PASTOR copy or photography portfolio galleries. I would love to be able to save a layout and reuse it across the site, and even across multiple sites. 
"Duplicate Page" is an okay workaround, but being able to create and save a landing page template would save me and many other designers HOURS of work.
Or, please just create some lead page templates and add them to the page templates when creating a new page.

It would be REALLY helpful to know what the roadmap is for SQS 7.1
We are looking at building a suite of new websites and love many of the features of SQS 7.1 but can't live  without a few of the missing features (import/export, secondary menu).
I understand that you are in development with this platform but some high level best guesses around feature set, timing and what will happen with SQS 7 would really help.
Danny

Unfortunately Squarespace are rather secretive around  v7.1 just like they are everything else. For me personally v7.1 can't replace v7 without some big improvements to the header, like you mentioned secondary navigation.
It would be nice to get some sort of direction or even stability from Squarespace regarding what they have planned but we probably won't hear anything until their test is over. But I know that they do plan on supporting v7 for some time to come, they just can't guarantee new features will make it to v7.