TL;DR
Higher levels of circuit wiring and multi-function combinators, based on and expanding on ideas here and here.What?
As technology in "the real world" improves, you get both increased capacity and miniaturisation. Electronics get faster, denser, and smaller. I propose a similar kind of progression into higher levels of circuit operation within factorio.More research would unlock expansion of circuit colours, multicore cables, the ability to read and write to different colour channels - some of these ideas have already been covered in the forum posts above.
I also propose a higher level of combinator with multiple functions and internal wiring. The recipe could be fairly advanced - 4 arithmetic combinators, 4 decider combinators and a processing unit for example, so as to represent that it's fitting the functionality into a smaller space rather than giving you the functionality for "free".
A mockup wireframe of potential GUI on the advanced combinator is in the image below. This would effectively increase the density of processing power at the expense of material cost, a reasonable trade up. It wouldn't make combinator programming "easier" in the sense of doing things for you. It would also probably still end up with large combinator stacks because, if there's one thing we know about factorio players, it is that they will keep adding to their factories until the functionality gives out.
Why?
It increases combinator and circuit network functionality while simultaneously making the top-level visuals simpler to understand and more space efficient.Functions that currently take 3 or 4 combinators could be pulled down to just 1 in size, while multiple colour channels and bussing would enable you to keep tabs of different inventory counts and perform operations on them either invidually or across channels without messy wiring and buffering.