I looked for a demo of progressive JPGs online and found this: https://pooyak.com/p/progjpeg/. Pretty cool
I cludged together a node.js application in 2013 to load JPEG SOS segments separately to the browser. The idea was to tie it to depth in a VR application, like level-of-detail maps in game engines, but 'online'. Turned out no browser like that much so I dropped the project.