Yes, my obvious alternative is to simply create a two layer submix for each of the six outputs and then just run clone of the files for each group of three and then use x,y shifting to achieve the goal. This is what I will do if I can't get this enhancement but as you can see, this only provides me with two layers per screen.

In all honesty, since my wall will be comprised of 6 screens, I was actually going to create three layer submixes each of screens (1,2) (3,4) (5,6) and then use the two remaining submixes as global. This is however more complex so not necessarily essential in my feature request.