How to handle "is_tablet" and "is_desktop" for convertible devices?

Aside from "is_tablet" reportedly mis-interpreted for some devices already and the question, if some "Ultra large phones" or "Pheblets" are Phone, Tablet or both, the new generation of convertible laptops like Surface or Surface Book (http://www.microsoft.com/surface/en-us/devices/surface-book) raises the same questions for the "is_tablet" and "is_desktop" attributes.

One may say both should be true. The UA is quite unlikely to change, especially since some like the Surface Book can simply be bent into a tablet rather than completely detaching the keyboard.