To repeat, what I understand about boxing:
A item-container, like a chest but not an entity (it has no active functionality, only when inside an assembly or other entity it is can be loaded/unloaded).
So it is basically a moveable box, that can hold one ore more stacks of items in it. (some restrictions may appear on that, for example limited to some type of items only, or not allowed to contain boxes itself for example).
TL;DR
Currently the mods, that implement it (TODO: set links to the mods), are limited to fixed recipes only, cause what's generated is basically nothing else, than another item. But if a box can contain more than one stack, it can be filled with different items. Of course. That would enable to pre-fill a box with the right number of items for the next step.
For example basic circuit production: I can fill a box with 1 iron and 3 copper wire to produce a electronic circuit out of it. Or much better: I fill it with 100 iron and 300 copper wire and produce 100 electronic circuits. Why not?
The assembly that produces elec. circuits needs only to look out for boxes, which contains needed items in it.
If - and only if - the number of items in the boxes/containers hit the right ratio (in this case 1 iron : 3 copper), the assembly can work 1:1 which means: It uses all items in a box and uses the same box to output the produced items.
For what reason is this useful?
The current gameplay with boxes is too complex: You need to handle around with different number of items for a recipe and so this mechanics of inputing whole boxes is complex, cause the number of input boxes is for most cases bigger, than the number of output boxes. So you need to handle around with full and empty boxes and that makes stuff really complex for beginners and for experts useless complex, cause you need to understand only once and then can manage this always in the same way.
But what's useful, is then some kind of repacker-station: Bring in created items in boxes (or single items only), repack them and use them for the production of the next step. E.g. red circuits.
This goes into a direction, where you have some kind of "Main Factory", where you bring in any item and some Outposts, where you can create >100,000 items per minute of copper-wire for example.
Longer description
What is needed:
- Packetzizer. A device, that is able to fill a box/container with number of item-types.
It can be filled via inserters from belts or chests of course, but I think it should also be filled via some direct belt input.
Input is then up to 5 belts (>9000 items per minute) and outputs one belt, for the overflow (it tries to avoid blocking a belt) or unuseable items.
It can work also as a requester chest, so it can also be filled by bots.
This device is able to fill a box/container with
a) either a given ratio of a recipe
b) any other number of up to 5 different items (a selection-interface like requesting items)
- Depacketizer. A device that is able to unpack a box/container with any number of items.
It can output the items of course again via inserters onto a belt or into chests. But output should be possible via belts. There up to 6 filterable output belts. If an item doesn't match any filter it will be output to the next unfiltered belt.
And it can work also as active provider chest.
- An assembly / furnace refinery, which is able to handle around with boxed items. Instead of inserting items we insert boxes. It can internally unpack the items. This can be made visible, like the box is then on top of the assembly. The stacks are emptied internally (just falling down out of the box). It can use up to 5 chests (one chest of one item type for example), but in that case you need to handle the empty chests yourself (filter the output inserters). If a box is available it will also be used to fill the produced items in.
Only for the case of right input ratios of a box, the assembly "resets" itself: it outputs the current items or the not yet fully filled box and then it uses the input box when emptied to fill the output box.
- Box/Container-types are then boxes with only one stack up to 5 stacks. Maybe more are needed. Maybe not.
More usages
The concept/idea of factory-streets (like in Star Wars I/II) is in my eyes only reachable with some kind of boxing, cause otherwise there is just too much afford to bring in the right number of items in the right ratios in the right order and with enough throughput.