One Word: Plastics

Plastic is perhaps the dominant material of the modern world. Concrete may be made in greater quantity, and steel may be more valuable, but plastic is omnipresent.
This could be reflected in-game by adding alternate recipes which use plastic to increase production. Plastic is used very frequently in construction as a membrane, meaning it could do well as part of a T1 or T2 construction part recipe (perhaps replacing iron with steel, too).
Household goods (personally furniture and tableware, mostly) should have a plastic variant as well.
Most especially, we should have plastic play a part in maintenance. Either add plastic to maintenance directly, or add plastic alrernate to electrical components.
If clothing or fabric goods are added, plastic fibers go without saying.
This will upset the balance applecart. It's probably going to need tweaking for some time. But consider that this makes for a very life-like logistical challenge of dispersing plastic to all its consumers.

Maybe plastic could be an alternative to wood in Construction Parts from Assembly III onwards, representing composite materials.

I guess, the devs intentionally didn't changed iron to more advanced materials such as steel or plastic, to make scalable use of it.
CPs and Vehicle Parts.
Otherwise, iron becomes obsolete right when steel becomes available. Which is rather early.
It is a little exchange of realism for game convenience.