Allow exits for underground belts to come up facing left or right.
So underground belts currently only allow you to go down and then back up in a single direction, straight. I think it would be handy to allow the exit piece to be rotated so that the belt could immediately turn as it came out. Currently you have to turn after you’ve come back up but this takes up an extra time and in heavy spagetti belt bases this is sometimes a little difficult/inconvenient. Underground belts that could turn as they come up would add that bit of extra utility to belts.... apparently that is a hot topic right now.
As I said, in this simple example this workaround is a proper solution. But if the circumstances ( surrounding machines / belts / ... ) are a bit different the underground belt in the green colored lane might not be an option. In such a case it would be nice to have an entry / exit for the underground belt that acts like a curve.
Factorio should not be a memory game that pushes you to memorize all kinds of workarounds. A "little" bit of puzzle game is okay. But I don't feel this should be the main part of Factorio.
RL: If my supplier of logistic equipment were not able to deliver such a simple modification for his bridge of material flow, I would start looking for a new supplier.
Radar : Damnit, we are surrounded!
Artillery : Great, now I can attack in every direction!
It's not a main part of Factorio. Space is practically unlimited, give yourself room to breathe when you're first building. I actually enjoy the challenge of fitting the puzzle pieces together to cram new things in, but when I don't want to think about that, my layouts have lots of open space in them.