I suppose you could level it and start from the ground. The Pantheon was first of all a substantial building. Its masonry construction when stripped of ornament and idols was useful for anything. This monstrosity would require much more financial input for modification than the alternative building a new cathedral would cost to be anything but a garish distraction. Of course the Modernists- those who are entertainment oriented wannabe protestants are surely thrilled with the prospect.
Monstrosity is what I call it, also. It has a look of cold arrogance about it.