TL;DR
Add belts with lanes going opposite directions.What
I order of my personal preference: replace green belts by that new belt type, add a new belt type or add a modding api to for users to create that new belt type.There is actually less edge cases than you would expect at first thought and to the best of my understanding this would not be the biggest of code changes, as belts already have two mostly independent lanes.
Why
When the green belts were announced i found even faster belts to be a bit boring. What if instead the two lanes of the belt went opposite ways?That would allow new and interesting builds, keep the same local throughput (you can just feed from both sides if you want to use both sides),
and automatically nerf long-range throughput, elegantly making trains more relevant there.
Now i do understand that it is unlikely to be added at this late point in the development cycle. I have checked out the mod-api and i don't think it is possible to add this idea as a mod (without re-implementing belts entirely). So it would be really cool to at least get engine-level support, even if it does not get added to the game, much like loaders and lane splitters.
side-note: viewtopic.php?t=4806 this is heavily outdated