At this point we have practical real world foldable devices. Maybe it is different for other people but I very rarely encounter them in the real world. I cannot help but feel that the feature is essentially a gimmick:

• The fold out screen is a secondary function. The device is invariably expected to be fully usable in folded state. This means that everything has to be usable without this secondary functionality.
• The fold out screen feature is always going to be more expensive, complex, and more prone to failure than a candy bar device with a single screen

The result is going to be that this will be a luxury or novelty feature without a compelling use case that absolutely requires it, perhaps similar to convertible touch screen laptops that can be used as an etsatz tablet.