This is a disappointing. Like Megan, we regularly use Story Maps for presentations to get people excited about the ArcGIS Platform. Being able to navigate the content smoothly, without leaving the framework of the Story Map, having to navigate back/and forth between other browser tabs or windows or loosing valuable screen real-estate, was a great benefit.
Not all of the Esri content has been broken yet in our presentations, however, do you know if this same best practice will be applied across all Esri sites eventually?
For instance, a quick check of one presentation shows that most of the content is still working, such as the Living Atlas (https://doc.arcgis.com/en/living-atlas/about/), Learn ArcGIS (https://learn.arcgis.com), and product home pages like ArcGIS Pro (https://www.esri.com/en/arcgis/products/arcgis-pro/overview) or Collector for ArcGIS (https://www.esri.com/products/collector-for-arcgis).
I'll also note that "http://www.esri.com" is the example text in the URL field in (all?) Story Map apps. So, if you enter that URL -- maybe this is your first time with Story Maps and you're just keeping things simple as you explore -- then it won't work.
Furthermore, most users won't have any indication as to why it's not working, as there is no warning or error displayed, they are just presented with a blank screen. They would have to be know enough to open their browser's console to find the error (e.g., "Refused to display 'https://www.esri.com/en-us/home' in a frame because it set 'X-Frame-Options' to 'sameorigin'.")
Perhaps Story Maps could being testing the X-Frame-Options setting for a site as part of the validation steps when you're entering the URL? Then you could let users know when they've entered one that is set to sameorigin, or otherwise restricted, and will not work.
