If the concern with second stairs is the internal hallway, then architects should eliminate that, not the other stairwell. There's no reason you can't have two internal stairwells connected to each unit. A former friend living in public housing in Toronto had a unit with good cross-ventilation, connected to both a stairwell at the front of the building, and another stairwell at the back of the building. Two units on each floor shared the stairwells.

As well, external fire escapes are still permitted by building code, and can be integrated into balconies. External spiral wrought-iron staircases are a well-loved feature of Montreal architecture, and would work well with a taller building with a single internal stairwell.