It seems the industry came up with various options to confuse monitor manufacturers, which is why there haven't been any G-Sync monitors put out on the market yet.
One involves Display Port technology, that apparently already supported the same function that G-Sync provides. This has never been implemented though, for some reason.
Then there is AMD's "Free Sync".
Apparently the technology has been there, but unused. So now a dilemma has cropped up.