I think this should be taken one step further - I think we should be able to have some manual control over the way the assets are loaded.
It could be kept simple with two actions and two triggers:
Action 1: 'load layout assets' - used to download the images of a layout. Works in the background while current layout plays, same as how the loader layout does.
Action 2: 'preload layout' - used to load images in a layout to the gpu (like the action CC has).
Trigger 1: 'layout assets loaded'
Trigger 2: 'layout preloaded' (both triggers take a string so you can tell which layout has been loaded)
With these actions/triggers, virtually all loading and pauses when switching layouts could be eliminated. Level 2 could download/load images to the gpu when level 1 is playing, or when the player gets to the edge of a level, make a 'loading' layer appear that could be animated, and go to the next layout when it's done.
I would really like to have this because it would help speed up previewing and initial start up times for players. 99% of the time I'm previewing, it's on one layout. If I could control it so the preview loads that one layout instead of the entire game and manually load the others when I want them, it would be quite a lot faster.
Similarly, it would also be useful to have 'load object assets'/'preload object'/'object assets loaded'/'object preloaded' to help stop stutters when an object is created for the first time and the game pauses as the images are sent to the gpu. But I think that's not as important as the layout ones.