I noticed in the maps2 example, the pano can open in a modal window by the showpano code. Comparing that with the Popup.xml code they seem quite similar but in my view the showpano is a better choice ;
the pano to be opened doesn't need an html file
the size of the modal window can be set a percentage of the browser screen
the lines of code is shorter.
The thing that is missing for showpano is a close button (X) which the popup actually has in option.
If you could add the close button to the showpano code that would be very helpful.
Or the other way round, if these 2 first features mentioned above could be added to the popup.xml as an improvement, that would make it much better.