I feel like the actual moral of the story should be "don't underestimate how trying to scrimp on a vital resource can result in horrible logistical complexities and a nightmare UX".

All true, but I would add that "in order to get back to the previous system that actually worked, you may have to provide a fig leaf for management, so that they can pretend no such thing is happening." We are back to one toilet per car, but we have to use cars of twice the size (with superfluous coupling in the middle that is never uncoupled) in order to pretend that we did not go back to the original system.

It's one of those parables with enough depth to support a ton of interpretations and morals

...which can be solved by a simple innovation, given the right approach.

Also, note how the shunting department was severely underequipped, "and it was only by virtue of the most cunning ingenuity, that they could just manage". Also sounds very realistic to me.

That, plus a manager inventing and enforcing specific requirements for dubious reasons, causing trouble in the company, and - as 'jancsika points out in their comment - quite likely introducing many new problems into the product.

Nah, it'd be more realistic if they were stuck with this expensive mess, and had to reverse all their work, and still had to do one toilet per car, because no one figured out this solution.

And the one guy who would have thought of this, they passed on three months before because he wanted 10% more in salary.

/cynicism

The more things change, the more things stay the same.