TL;DR
Create assemblers that are single object (mega assemblers) built from multiple assemblers, inserters and storage chests, that place on the map as single items, but allow parallel stages of assembly so a single large object can produce multiple objects or single objects that requires multiple assembly steps.What ?
Create multi-assemblers that allow for the production of multiple items.The 'multi-assembler' object can be built once the tech has been researched (a tech and multi-assembler for each level of assembler tech?). This would be an assembler that works as a single object producing multiple items using multiple production slots. The items produced could be all the same - every production slot producing say, yellow belts, or they could be set up to produce the sequence of objects required for a final product - all the parts required for assembly machine 3s.
The image below offers a suggestion how the user will specify the production and allocate the storage.
The user selects the production slot at the top and chooses the production for that slot. At the bottom they can specify how the available storage is to be allocated.
I suggest that these will be built in assemblers, with the ingredients being assemblers. inserters and storage chests (and modules on the level 3 mega assembler?).
I suggest that we could have different sizes of multi-assembler. Assembling machine 1 based multi assemblers can have 3 production slots. Assembling Machine 2 based multi-assemblers could have 3 or 6 production slots .... and 3, 6 and 9 slots for Assembling Machine 3 based multi-assemblers.
We could, perhaps, expand the idea to include the addition of furnaces and / or oil processing to the multi-assembler, allowing the user to build multi-assemblers with whatever production unit he/she wishes. The user can specify a 9 slot multi-assembler and add any machine into each slot. They could then use this to process uranium (8 slots) with a slot running kovarex, or they could have a refinery and chemical plants ...... The icons on the top of the machine would be like those for a blueprint. - If we were to include refineries or uranium processing, those objects would be included in the ingredients, and we would add items like pipes and storage tanks also.
Why ?
The task in early game would be the same as it is now, that you have to work out how to produce items using belts, assemblers and inserters ... and that would not change. Later in the game, once you have worked out the issue, simply repeating the arrangements you already have is a trivial task .. (assuming you have bots). These machines would provide an additional route to achieving production and would offer the player a choice of how to proceed. Do they rip up their existing and use 'elegant' multi assemblers (assuming they can work out how to organise the production within such a machine) or do they leave what they have?I can also see that these machines could be 'nested' together to work in parallel, to combine the multi-production of the machines, passing resources back and forth between them to expand the complexity of items that can be produced.
The multi-assemblers therefore provide an additional avenue for exploring the optimal way to build your factory ....
Do I build a mall with individual machines, or do I use a smaller number of multi-assemblers .... ??
I expect there will be a small benefit in reduced graphical load due to fewer items displaying (and moving).