The slow strips on the outside moved at five miles an hour; the inner ones faster and faster...

Not good enough. The same strip should go faster and faster over time and decelerate near its end. It sounds impossible, but I can think of a few ways to make it work.

The naive implementation is a train: everybody enters at once at a fixed point, the strip accelerates, everybody leave at the next stop or stay for the next stop. I wonder if you devised a way to make people keep accelerating while other enter and leave the strip. Side strips at lower speeds are too easy a solution.

One of the videos in the article mentions an accelerating moving walkway: https://youtu.be/CMlLPgAL2h0?t=240