Edit: DIsclaimer: I tested it on a bus. It will only work with a modification and stacked boxes maximum allowed items pers box is 3 and all sorters need to have filters so there is a sorter for each item type from box pillar to box pillar. With 9 items it means boxes need to be 3 high. And it will get higher with intermediate products.

The Dark Fog Update opened up an incredible mechanic that was not possible before due to overflow problems, and inputs filling up slots that we wanted to use otherwise.
That restriction is now gone.
It maxes things like 9 inputs/ belts possible. PER LAYER. At a maximum of 8 build height that is an insane number of 72 different items. Boxes now also make item elevators a real and easy possibility.
The only restriction is your sorter speed. Inputs and outputs of assemblers/smelters can now easily be realised, however it limits the machine to only 2 input sorters.
In the case of my example here is how it works. Set your recipes in the assemblers, for example a mall. Note down the input items. All your connected machines should have a maximum of 9 different items. Adding one more layer is possible, and I've done it in my matrix hub not only for one more layer but 7 in total. This example is slightly different though. This method actually makes it possible to route 27 different items through a build height of only 3 and in this dense configuration I show here.
The major downside will be the extreme buffering of items because each stack will hold its maximimum when it is backed up. That means on a long bus with expensive items like quantum chips you will have a thousand chips on a height of 1 and a length of 10 (which would still enable you to build a 21 machine bus.
One other main advantage is that the assembler can draw from the box with full speed as if it were on a close belt. That means that 3 different (or more) items could be pulled from that side without distance restrictions which will make timing machines alot easier.
However I have not tested it to that extend and am not 100% sure how sorters are prioritising and if the assemblers pull items out into the next box or if assemblers grab their stuff.

The beauty is even if the box has 30 different items in them the assembler magically knows what it needs. And since we now can lock slots the boxes will never overflow with other things and brick the system.
This will make mall designs super trivial now. All you need to do is create a lenght of smelters first that produce rings and ingots, then machines that do coils and gears, and progressively go through the tiers. Set one slot for each item in the chain in every box from the beginning. That has to be done only once, since the filter can just be copied like a recipe from a machine.
And voila, your super narrow tiny small bus mall is built. The beauty is you can do anything with just a titanium stone silicon iron coal and copper input. Even oil if you so desire, or sulfuric acid and water. Sadly those are exactly 10, so you have to ditch one raw ingredient. 
But you get the idea what is possible with this. I hope.