[ardecila]

It's not clear to me that Ogilvie could host MD-N, MD-W, and NCS in addition to UP-N and UP-NW which can't be rerouted. That's a lot of trains, and more importantly a lot of passengers. The concourse space available at Ogilvie may not be enough for the peak crowding and potentially unsafe in the event of a disruption. On the flip side it leaves the north end of Union under-utilized, and it's not clear what new services would fill the void (Rockford trains?)

There's also a vague plan for frequent (20-minute) service from Union Station to O'Hare, which would need to cross over at A-2 in any case.

I guess if you rebuild a fourth track from A-2 to Pacific Junction you can separate MD-N from MD-W and NCS, and send only MD-N to Ogilvie while sending UP-W to Union.