Rob Millar commented
It would be great to be able to scale the preview window to defined display sizes. For example I could be designing an interface for a 7 inch display with a 800 x 480px resolution, but then also designing and interface for a 5 inch display with the same resolution.
When I come to preview the design, I have to manually scale down the preview window to an approximate 5 inches.
It would be really useful to have the ability to select what size the preview window should display at and the ability to create custom presets too.