It seems a good approach to layouts would be to allow the user to only use the elements within the scene its connected too. But being able to place, resize, those elements differently in each layout.
This would save a lot of work, especially with unique ids, which you need to change for each layout, and then the code.
Of course you cannot have duplicate IDs, so when it's exported and hosted, it knows the screen size, and loads the correct layout, leaving the others out, so not in the browser stack.
Is this possible ?