I can confirm that Chris’s code edit above makes mapping sub pages possible.
This would be a great addition to your plugin.
This allows people to make a microsite with more than one page.
Lets say your main site is https://www.widgets.com
You want to make a training website for showing customers how to use your widgets.
For this, you purchased https://www.widgettraining.com
Rather than install a whole new WordPress site or enabling a multisite for this, we could just use your plugin to route the new doamain’s traffic to a specific page on widgets.com
With the default plugin functionality you could map the domain:
https://www.widgettraining.com
to route traffic to
https://www.widgets.com/training
With chris’s edit above, you can map sub pages to expand the microsite like mapping:
https://www.widgettraining.com/widget-a/
to:
https://www.widgets.com/training/widget-a/
With body class CSS and page templates, you can then give the look and feel of an entirely different site on the same installation of WordPress.
Add the following plugin to change the nav menu per page:
https://www.ads-software.com/plugins/ce-wp-menu-per-page/
As a reminder, you need to include www and non-www versions of your mappings to cover all traffic routes.