Probably not going to happen.
<snip other stuff >
Metal rails seem vaguely modern, going by our favorite dubious source, but I'm not as opposed to them as I am to steam locomotives and light bulbs and nuclear reactors, since dwarves should be capable of using metal if it's around.
I was thinking of that quote (or one like it) when I was watching my miners/stone haulers/catapultists yomping over from one end of the map to the other, and pondering how a monorail would make that a bit more efficient. (And of course wishing that I had an extinct lava tube that I could run it through, and cap with a sliding roof capable of at least temporarily fooling airborne spies.
But back to the 'reality': that'd be a stone-carved monorail/monogroove, if necessary, and with all this talk about steam pipes mirrored my own idle thoughts at the time about giving it an 'atmospheric engine' propulsion method. (Though that then quickly led to a "steam catapult" idea, and ultimately led to to a 1400s-style MAC weapon to add to the (anti-)siege weaponry.
But as it has been discussed before, so it shall be again. You may take this merely as an idle musing along the lines of the idea, by pure coincidence, once again running amok through my mind at about the same time as the above was being posted...