I would love to have the ability to change the opacity of a layer; either as a separate node itself or as part of the "Combined Layers" and "Combine Layers with Transform" nodes. If it were a separate node it may make sense to combine transform and opacity feature into a single node and then get rid of the "Combine Layers with Transform" node as it would be more or less redundant.
This new feature would give the ability to dissolve layers completely in and out or partially for more semi-transparent graphics over images and video.
A node that is similar to Arrange Layers in Grid however differs by simply grouping all layers together as close as possible.
Node could allow choice as to concatenate layers vertically, or horizontally, and also how they are aligned: top, bottom or center.
This would be great to easily create UI elements and controls grouped together that are different sizes or lengths. Think of having a Play button next to a Time Slider UI. The Time Slider will be long yet the same height as the play button.
By grouping these together it would make UI design simple and easy to change onthefly, or while a program is running.