Given that there are two escalators per direction, making the middle ones purely for walkers would probably create the necessary incentives to get ~2/3 walking to bypass the longer queues on the sides..
Well, the point of the article was that if people are standing on one side, you've only got half efficiency, so if they take a whole escalator and make it walkers only and double up the other one, nothing is gained. At least if the outer was stand only and the middle was current rule, there's a 25% increase.
I think the article is missing the obvious point that the queue at the bottom affects walkers as well as standers even though it is being formed by the delays caused by standers needing more time on the escalator. Allow walkers up the middle well separated escalator without interference and many more people would walk.
I doubt it. Even if you are relatively fit, many of these escalators are equivalent to 2 - 3 flights of stairs, after sitting standing in a hot carriage for 30mins plus.
The speed that you are expected to ascend as a "walker" is high. I know, because I used to climb every day, and I would get disapproving noises/looks if I failed to climb with sufficient speed.
That doesn't apply everywhere - e.g. Cutty Sark DLR only has two escalators and I can think of a few places which have three shared between up/down (split on morning/evening peak traffic.)