Is it possible to use the Microsoft Band SDK in Unity 3D? I haven't heard any official word on it and I'm wondering if this is something we are waiting on Microsoft to get around to or if both companies have to work closely together to accomplish this. Due to the way Unity builds your project data to specific platforms, I highly doubt you could simply add the SDK to your project through Visual Studio and actually make use of it. I am writing C# scripts which are compiled by Unity. I want to take accelerometer readings and place a tile on the Band to interact with the app, and I want to build my project to UWP and Android, and iOS if possible.
The Band SDK targets native Android, iOS, and Windows so you won't get support within Unity 3D "for free". There are Xamarin bindings for the Band SDK that allow its use cross-platform in Xamarin-based apps. You may be able to use these bindings to use a Band within Unity either directly, or indirectly by creating a plugin which wraps them. If not, you may still be able to create a native Unity plugin that wraps use of the native SDKs on each of the platforms you intend to support.