As the title says, I think that the game could benefit from having a sorting bloc that is bidirectional.
For exemple, a situation where this would come in handy is between the main inventory and the constructor so that you can blacklist ingots, but allow components to pass through. This could also be useful for 02 H2 tanks which need to be able to pass both ways from your refill location back to your inventory. Small containers being used as access ports could also benefit from this. In that situation, the goal would obviously be to push anything deposited in the small container to the main inventory while still allowing access in the other direction. This would reduce the size of conveyor systems.