The cost of doing all that sounds like it would be higher than replacing what exists now. Right now autonomous vehicles that exist are either production cars with stuff added to them, or fancy enclosed golf carts, so the MTA would have to single handedly develop a completely new type of electric robot tunnel bus, along with their batteries, charging systems, and navigation software. And it would have to spend years tearing up the existing tracks and redoing stations and then putting in pavement and charging facilities.
Also someone tell this guy that automated metro trains already exist and are standard on new metros in China and Asia and they build new lines for cheaper than we can fix old ones. So maybe the solution is to reform the agencies in charge of infrastructure and seek wisdom from countries that don't suck at these things like we apparently do.
What that article describes has been a concept in urban transportation since the 1970s. VAL systems, the Morgantown PRT, the
Pittsburgh Skybus, etc.
To match the capacity of a subway train, such a fleet of autonomous vehicles would have to basically be a bidirectional bus with multiple doors, longitudinal seatings, etc. In other words, a subway car. The electric motors would need a way of charging, so third rails would have to be installed along at least part of the line. Meaning there would still be a lot of complex infrastructure to maintain that would degrade over time.
I assume the entire benefit of this specific plan really comes from being able to add and subtract cars and send some of them down other routes per demand(hence the whole privatization angle). But where would empty cars go to turn around or wait if demand was uneven? Wouldn't there be congestion as vehicles accumulated in midtown during rush hour? Software might be able to optimize the network into a humongously complex interlining scheme but the physical constraints of the tunnels and where they go would still limit things.
The nice thing about the rails is that they and the rolling stock that run on them are already in place and are probably the longest lasting component to the whole system. Automated vehicles would still need to have charging stations along the routes which would need power conduits. The tunnels and stations themselves have to be kept up.