Android Studio 2.2 Preview all screen sizes missing
The option to preview all screen sizes is not available in Android Studio 2.2 Beta 2. However, you can resize the preview screen to see how your layout would look on different screen sizes, as shown in the attached gif.
While preview all screen sizes seems to be gone, it is possible in 2.3 to view more than one screen size at the same time.
Right-click on the activity_main.xml (or whichever xml file) tab, and from the pop-up menu select split-vertically or split-horizontally.
This will create a second xml tab that can use a different screen for design/text. This can be repeated for more tabs, and the tabs can be "torn off" to float separately.