A fucking built-in genlock? For years I thought only Amigas had those!
Put on the die, but only expose on the $$$$ builds using it?
Maybe it's buggy or something? Unreliable? Use causes overheating or RF interference issues?
Maybe IBM added it for project X, and then project X got cancelled, and everyone else forgot it was ever there...
The article mentions that it is brought out to the connector, multiplexed with the monitor ID pins.