Microsoft's mobile business has been in continuous decline for some time now, and the company's silence over the future of its smartphone efforts has frustrated even its most ardent fans. A big question mark continues to hang over Windows 10 Mobile, after the company axed its support for all but 13 devices, and broke away development of the mobile OS from the rest of Windows 10 into a separate 'feature2' branch, which has so far seen no new features or significant improvements in recent builds.

This has led to a great deal of speculation over Microsoft's plans for Windows 10 Mobile, and many have questioned whether or not the company still intends to launch its much-rumored 'Surface phone', given the continued dominance of Android and iOS in the mobile market. The fact that Microsoft recently began selling Samsung's new Galaxy S8 and S8+ Android flagships in its US stores has only added to the uncertainty surrounding the company's plans for its own mobile devices.

Today, Brad Sams posted details gleaned from well-placed sources regarding Microsoft's plans. From my own sources, I can confirm at least some of the information that he posted, and I can also add some further details to what he revealed.

Brad reports:

Two independent sources inside of Microsoft have told me that there is a new hardware device being tested internally and that there is also a separate branch of Windows Mobile for this device.

I have heard the same information regarding a new mobile device being actively tested, although details regarding the actual hardware have been vague and far from concrete. As recently as three weeks ago, I was told that Microsoft has also been testing new Windows 10 builds on existing high-end third-party hardware, including HP's Elite x3.

Brad also referred to "new experiences" for Microsoft's own mobile hardware, adding:

Additionally, the UI is expected to be different than what we know today as Windows Mobile but the exact changes are still evolving as we are in the early days of development of this experience.

My understanding, from three separate sources, is that this new 'mobile experience' being tested isn't a new Windows 10 Mobile branch, but rather the 'full' Windows 10 OS with a UX scaled for mobile devices. These efforts are part of CSHELL, an 'adaptive shell' that can scale the entire Windows 10 OS for the type of device or display size on which they're running. CSHELL (an abbreviation of 'composable shell') will eliminate the need for the separate Windows 10 Mobile shell that is currently used on smartphones.

Twice in the last six weeks, I've seen CSHELL builds running on Windows phones, looking a lot like Windows 10 Mobile, but with some noticeable differences, including changes to the notification center, and some tweaks to the Start screen and apps list. The builds I've seen were both at an extremely early stage of development, and while they were both usable, it was clear that they were far from feature-complete, and still in need of a lot more work. As that development continues, it's likely that the UX will change, particularly given Microsoft's recent announcement of its new Fluent Design System, which did not feature anywhere in the OS builds that I have seen.

Microsoft hasn't shared its plans for CSHELL, but what we know dovetails with information that the company has publicly announced. In December, Microsoft revealed plans to bring full Windows 10 to next-generation ARM devices, with support for x86 desktop apps through emulation. Microsoft has only publicly commented on these plans in reference to ARM-based 'cellular PCs' - i.e. notebooks with integrated 4G LTE connectivity. But as the company continues to phase out its support for existing Windows phones with major Windows 10 updates - and with vanishingly few hardware partners continuing to support Windows 10 Mobile as well - its CSHELL development efforts point to a longer-term vision for mobile devices.

When you combine CSHELL with the Windows 10 on ARM announcement, and add in the knowledge about the company working on new mobile hardware, the bigger picture begins to come together, aligning with the recurring rumors of a 'new class' of powerful mobile device, building on Microsoft's PC-like Continuum vision for mobile devices. But that's only part of the story - for those who currently own Windows 10 Mobile handsets, there are still many questions to be answered about how that future will play out for them.

The answers to those questions are currently less clear, at least based on the information that I've been provided. In February, Microsoft committed to releasing further Windows 10 Mobile builds "beyond the Creators Update", and it's honored that promise with its recent 'feature2' Insider Preview builds. However, two separate sources have told me that feature2 is effectively the 'end of the road' for Windows 10 Mobile, and that the decision to split its development away from the main Redstone 3 Development Branch reflects that reality. Both sources likened feature2 to the Windows Phone 7.8 update that Microsoft released for handsets ineligible to upgrade to Windows Phone 8.

One of those sources added that feature2 will eventually roll out as an update for all supported Windows 10 Mobile handsets (although I've been unable to independently corroborate that), and that it will include new features - perhaps including Night Light and the new Continuum improvements that Microsoft previously announced, among other additions. Separately, Microsoft's Brandon LeBlanc publicly revealed this month that new "features for enterprise customers" are coming "later this summer".

Two sources have also indicated to me that they don't expect any further feature updates to Windows 10 Mobile beyond feature2, suggesting that the company will focus more heavily on CSHELL and Windows 10 on ARM after that point, while continuing to 'maintain' Windows 10 Mobile with security updates and other fixes. At its Build 2017 developer conference, Microsoft said that the Fall Creators Update will come to Windows 10 Mobile, but that update may still come from the feature2 branch, rather than the RS3 update that will roll out to PCs and other devices under the same Fall Creators Update name sometime around September.

No-one that I've spoken to has yet been able to offer a definitive answer regarding Microsoft's plans for supporting existing handsets in the longer run. While Microsoft has been testing Windows 10 CSHELL builds on some existing devices, that's no guarantee that those devices will be officially upgraded; Microsoft may well prefer a completely clean slate, only supporting its updated Windows 10 experience on entirely new mobile hardware.

Brad also reported today that Microsoft may discontinue support for Silverlight apps on mobile devices running the updated OS, so it certainly seems the company is open to leaving behind at least some of the mobile platform's existing assets, and moving on to newer, greener pastures.