TL;DR
Add extra mode for train stop to make train which is already on the way to the station do the stop at this station but don't allow other trains to select this station as destination.What ?
At the moment station can be either open or closed. I'm suggesting to add one more state - "No schedule", for trains which are looking for stop it would look like closed, but train which is already on the way to this station would be able to make stop on this station.If train which is going to station in "No schedule" state is rerouted because of busy track or anything else then this train should ignore this station.
"No schedule" state should be able to set via Circuit network, like it is done for enable station now.
Stop should send amount of trains heading to this station to Circuit network.
Why ?
This change will allow to build complex rail networks using vanilla game.Extra state with extra signal will not break any existing setup, but will give flexibility.
This change isn't contradicting with game principles as trains are aware about closed stations instantly which means that there is some feedback loop between train and stop.
Example
Train 1 is loading ore in station LOAD, Train 2 is waiting.Train 1 going to left UNLOAD because it is closest station, unload station circuit switch state to closing, Train 2 going to LOAD station.
Train 1 is on the way to UNLOAD, Train 2 selecting right UNLOAD station as destination, because left UNLOAD is closed for scheduling.