The problemBy far the most annoying part of Factorio, responsible for the vast majority of my abandonments of it over the many years since I first found Factorio, is the tediousness of rotating and placing belts and pipes to go places (the quickbar has substantially reduced this annoyance level, leading to my second ever rocket recently ).
The solutionThen a couple of days ago I discovered the awesomeness of the rail planner! Clicking shift allows a train track to automatically be routed from point A to point B, dodging all obstacles: Something similar for belts, underground belts, pipes and underground pipes, would be wonderful; avoiding the unpleasantness of careful click+dragging (and failing to get that exactly straight line, requiring removing that belt/pipe), mashing "R" many times and repeatedly having to switch from underground to above ground to connect resources. And, of course, repeatedly screwing it up and having to remove the ghosts/items that have been placed.
ImplementationIn implementation I'm imagining it working exactly like the railway planner, you hold shift and click on the edge of an unconnected belt/underground belt/pipe/underground pipe while having selected the item you want your route to be made of: Then move your mouse to your destination and Factorio will then show you the ghost route (imagine the belt is green like the railway tracks in the following screenshot): Click again and all the ghosts will be placed (displayed like the above image).
If you have selected the underground belt, the route should be made of underground belts where possible, only using normal belts for the corners (Naturally, selecting non-underground belts will result in more circuitous routes as it goes around all obstacles): This won't interfere with any existing workflows because shift clicking on an existing object currently doesn't do anything.
Related enhancementThis would also be very helpful to have for small, medium and big electric poles. No more having to make train track+power line blueprints and carefully pasting them, just designate start and end points for your big electric poles and start and end points for your train tracks!
Business valueThis would be THE biggest Quality of Life improvement I can think of for Factorio and would have prevented me repeatedly abandoning it in annoyance. No joke, this would approximately double the fun and value-for-money for me (I will literally buy two more copies of Factorio to give to friends if you implement this).
Despite repeated searching I haven't seen this suggested anywhere, even though it seemed like an obvious feature...