At Build developer conference today, Microsoft announced that they are introducing a new Windows class that will allow developers to easily include multiple windows support in their UWP apps. Previously, developers have to write hundreds of lines of code to add multi-windows support in their apps, but with this new Windows class, developers can do it with just a few lines of code.
Previously, each new window opened will be running on a separate thread, so developers have to dispatch everything to the new thread, etc. Now, Microsoft is allowing developers to have their newly opened windows in the same thread, making it simple to implement. Of course, the old way of having new windows in new threads will also remain supported.
In addition, Microsoft is also making it easier for developers to add fly-out windows in their apps. These new improvements will enable developers to easily add color picker, contact cards, and other such scenarios in their UWP apps easily.
These new APIs will be part of the upcoming SDK which will be released in Summer.