This is just off the top of my head, but what if killing a train depot down to a certain level (25%?) makes the convoy/train resupplies 10% slower to any strats or fields? Or even if the roads/tracks aren't implemented in the map, that time delay for resupply shipments.
10% might not seem like much, but if you need 4 to 6 convoys or trains to fully resupply something, that will add up to a noticable delay and help your country's base taking efforts down the road.
I believe 25% is too high. 20% would be a better choice, or even lower. Mind you, this is coming from someone who LOVES to hit strategic targets. I want my run to make an impact, but I don't want it to be too easy for me to inflict serious damage to the enemy's industry. Don't take it to a Capital's difficulty, but definitely not have it as easy as the old strategic system was.
A Complex Version:
What if the delay is based on the condition of the rail yard? At 90%-70%, there is a 2% delay. At 69%-40%, 5%. At 39%-21%, 7% delay. At 20% or less, you have a full 10% delay.
And what and how would you precisely have these supply routes do?
Also include all rate controls.
P.S. if you can just hit a static target (i.e. bridge) what is the use of having the supply route?
HiTech
Rail Yards could cover the spawn times of a convoy. From what I can tell, there is currently no way to delay the spawn time of convoy's. The Convoys always spawn at the same time (they spawn more often if a base is damaged), regardless of the status of strategic target's they are tied to. This would add another aspect to the strategic war effort. You can inflict damage to the supplies produced
and/or the time it takes for them to reach their destination.
Slightly off topic but; Any word about your idea of a Concrete Factory? I remember you mentioning the possibility of adding a factory that affects the down times of towns. Maybe it could also be tied into the down time of the Rail Yards? That may make that bit complicated, (EDIT) having the factory for town times tied to the rail yards...