Just ruminating here about what a completely robust system would look like.
If I had my druthers, I would design a twin system. Each central system would be located apart from the other - say Atlanta for one and Cleveland for the other, in the case of NS. That would mitigate problems with weather. Both systems would be operational, in order to share the workload, but be capable of taking over from the other system, if it went down. Communications between the systems would be such that there would be no single point of failure.
Ah, but I can dream, can't I?
jb