It’s still pretty narrow, because the individiual stairs themselves are only about one to two people wide, and they’re far enough apart that people would probably ignore any left/right directional flow that you would see on a double-wide set of stairs.

To give some perspective on how long a reconfiguration like this takes, JR East has been working on platform optimization like this at Shibuya Station since 2015, and the last elements will complete in 2027; and that’s at a station that started more optimally than Penn Station.