Must be a single uninterrupted folding screen. It must run Linux about as smoothly as on a normal laptop; a couple minor bugs or stutters here and there are fine, but it needs to be a reasonably reliable practical computer. Must support the same portability features as normal on foldable laptops, like touchscreen, rotating display, external wireless keyboard, on screen keyboard, etc.

It doesn't have to ship with Linux, but Linux must be installable with its normal installation process, not hours of configuration to get it working on that particular device. (No, "hours of configuration is the normal Arch installation process" is not a valid argument. It has to be a user-friendly distro.)