Microsoft's device roadmap has been leaked, and it contains a lot of information about upcoming devices. The most interesting one is the mythical pocketable dual-screen Andromeda.
They do, however, say that Andromeda, Microsoft's mythical pocketable, two-screen, hand-held device that's supposed to carve out a whole new market for itself, is due for release in 2018. The documents also say that, after Andromeda, Microsoft OEMs will produce their own comparable products, just as they've done with Surface Pro.
The big question for Andromeda is the same as it has always been: why? To define a new hardware form factor, as appears to be the intent, its design needs to be particularly suitable for something. Surface Pro, for example, has appealed particularly to groups such as students (taking notes with OneNote) and artists, thanks to its form factor and multimodal input support. To succeed, Andromeda needs to offer similar appeal - it needs to enable something that's widely useful and ill-suited to existing hardware. But presently, there are few ideas of just what that role might be.
From what I understand, it will look something like this, and its entire UI is Modern/Fluent Design/Metro - there's no Win32 here, no traditional Start menu, and so on. With the device being pocketable, my biggest open question is whether or not it will have phone functionality, effectively making it a Surface phone, and a new attempt at breaking into the smartphone market.