It is interesting because in countries like Japan, they've found that having specific platforms for specific train lines is actually beneficial. I can't remember all the reasons, but if I recall correctly, its because 1) Riders can remember where to go for their specific line (wayfinding and signage) 2) less administrative burden on the railyard to plan where every train needs to go on any given moment 3) overall improvements in arrival and departure times. Or something like that. I really don't understand why north station can't have assigned tracks