I would like to see a way of modifying a particular layer's attributes on all layouts simultaneously , if that could be possible. Global GUI objects work a treat, but layers are useful for so much more than just a HUD - and each layout has to have the same number of layers for the technique to work and so they don't 'get lost' as the player navigates around (unless I'm missing something really obvious). Thus adding an interstitial layer or changing attributes like effects, scale rate and parallax etc becomes a pain if your project has many layouts.
So, I would like to be able to select all layers with a particular index number in all layouts at the same time. Changing common attributes would then be a piece of cake. Imagine how much time this would save on a project of 30+ layouts....