We've found that exporting a large site is difficult through the user interface and perhaps impossible with login-to-view. A plugin that initiates a download could be required.
Say EXPORT to create an export format file. Could be other formats someday that includes assets.
Say ORIGIN to download the entire origin site. Could offer input field or mayb export whole neighborhood.
Say FORKED to add a fork action to each page. We don't do this now but could. Will give ups a date for each page.
Download will create a file in the downloads folder named according to the sites hostname. We depend on the client operating system to date files and number duplicates.
Drag exported file to a new site to selectively upload as we always have.
A utility page Export Backup will join other pages in the web page footer hamburger menu.
Current practice is to click or curl export.json