Sure but should it be the same in a game just from the beginning?
Never forget the ‘easy to learn, hard to master’ … So a basic way of manufacturing at the beginning is okay for me. There is enough to learn even if you don’t have to take care of preassembling.
I agree in case of later gameplay. It would be great to have several things - not only the doors but e.g. the body, engine and wheels too - split away from the main production line into spearate subassembly lines. But before talking about this better talk about how much simulation and how much simplification is needed. Of course a sedan has four different doors and not four of the same …
In my mind there is no need to simulate even the smallest bolt and piece of cable.
So Yes to a bit more detailed production process, Yes to subassembling but also a strict No to have an overwhelming level of details right from the very first moment of the game ;o)
[Edit] But back to topic: The Fit Windows slot has the same issue as the slots that are available on start: It can’t hold enough parts for two processes. In combination with the suggestion of a 1x1 stockpile maybe a researchable expanded slot stockpile - so 32 instead of 16 items can be stored at the cost of 4 instead of 3 tiles space needed - would fit everyones need?