Allowing the Speed Dial page to shuffle through a "folder" of selected wallpapers whenever a user opens a new Speed Dial (or on a timer) would add refreshing value to the experience, as well as maintain a consistent wallpaper functionality with modern software.
Currently you can only have one wallpaper selected which is lovely, however modern operating systems are setting the precedent that users can now have the background change dynamically over time from a selected folder or group of images.
The observation of seamless integration and consistency between a user's OS and their browser would be further solidified in the user's mind if Opera mimicked this behaviour; this experience is valuable and improves the overall feel of using Opera.
The quality of life improvement by having this small feature would give a freshness to the browser and make it feel more like a dynamic, living piece of software. Preventing it from feeling stale and monotone like other browser's who do not have this functionality, setting Opera apart as a browser who trail blazes and sets the standard as a browser with excellent user experience.