Quote - If the background feature properly uses an equirectangular image, then this would be great.  In my experience with this function, it only places a flat image file behind the render selection.  I can't even pan around the image (unless there's something I don't know).

That sounds more like backdrop than background... When I put an equirectangular image into a background, I can pan around it without any problem. If you change the zoom of your camera lens, you'll see different amounts of the background, too.