The Adaptive UX initiative is controversial: Many devs are skeptical that Microsoft can produce a UI Veg-o-Matic that adapts a single app intelligently to different screen sizes. It's particularly controversial for experienced mobile developers, who are accustomed, begrudgingly, to hand-tuning UIs for every conceivable screen size. The jury's still out.
A Windows Dev Center post goes into great detail about many of the new APIs, some of which are still experimental. There's strong interaction between custom apps and Windows itself in such areas as drag-and-drop, encryption, power conservation, Wi-Fi and Bluetooth, HTTP live streaming, location tracking, and ink panels. There's even an IsWindows10OrGreater function.
Microsoft product manager Cliff Simpkins talks about highlights in the new SDK in his Building Apps post. Those of you with older Metro apps, er, Windows 8.1 apps might give these a try:
For developers with an existing Windows 8.1 app, you can quickly try [Adaptive UX] out by (a) removing one of your UI projects (and going from three Visual Studio projects to one!) and (b) add the improved ViewStateManager to control how your UI adapts at runtime... Start checking, at runtime, if a Windows feature is available on the device before you call a related API. A good API contract for you to try out in your code to see this in action is HardwareButtons, which is present on phones (via the Mobile Extensions SDK), and thus available on the phone and mobile emulator but not available on the desktop. We believe that API contracts and the extension SDKs will allow you to adapt your code at runtime to deliver user experiences that feel right on the device it's being run on.
Windows 10 Technical Preview supports "old" Windows 8/8.1 Metro/universal apps. If you need to continue supporting those apps, you may have to resort to conditional compiles. On the other hand, if you're going Windows 10 only, your app can cut the #IF's and use the new Adaptive UX code, for hardware-specific tests at runtime. A word to the wise: This being a beta, you may well see different behavior in your old apps running with the new SDK.
Finally, S. "Soma" Somasegar, corporate vice president of the developer division at Microsoft, posted an MSDN blog highlighting some of the key differences in the Windows 10 SDK:
Sign up for CIO Asia eNewsletters.