Is there an online video server that can show paneable extremely large videos?
With current technology no, you "can not"; and with more powerful technology it is a waste of resources.

You do not need to stream a gigapixel video, you need to stream a video, receive the new "interest" zone, process the coordinates and display a new version of the video. Even arrange different chunks of different videos.

This is what google maps, bing maps or other applications do. They do not send you all the photos of the planet, just the ones you need.