Recently, the US Trademark and Patent Office announced a new patent, which was applied for by Microsoft. The patent shows that Microsoft has added a secondary screen to Surface, which was filed in May 2017 under the name "REFLECTIVE DISPLAY" ("Reflective Display").
This patent we see, Microsoft introduced a second display for the Surface, this screen is mainly supplementary and other summary information. As described in the patent, this secondary screen displays information through a multilayer reflective structure.
Microsoft's multi-layer reflection through a polarizing film, diffuser, and illuminated screen ultimately reveals information on the back of the Surface device. Of course, as one of Microsoft's many patents, we are not sure whether this technology will be used in future Surface products. However, if you have a dual-screen blessing, the Surface product may be more fun.