The crease in the fold should be non-existent: no color bleeding, no weird reflections, it must be a perfectly flat screen. Apple extremely picky about image quality.

Also, water and dust resistance must be amazing.

They already sold a phone with a folded screen before (iPhone X has a fold at the bottom to hide control lines), so they may be looking at the tech with a different use case in mind.

For example I could see them looking at foldable screen tech to make the bezel disappear (iPhone X screen trick, but taken to the extreme).

Picture an iPad/iPhone which is just a perfectly flat piece of screen, no bezel (or a very thin one), no notch, no edge aberrations (like the curved screens some smartphones have). Essentially Job's vision.