TL;DR
A modifier to the train wait conditions, to apply them to one, multiple, or all wagons.What ?
e.g. Instead of saying 'Cargo is empty', or 'Cargo is full', we can specify 'one wagon is empty', etc. Obviously not all existing conditions would work with per-wagon basis.Why ?
Increases flexibility of train routing, at minimal effort.Haven't seen this one in suggestions search - apologies if it's been suggested previously!