That completely depends on how graphics intensive a particular game is. Sure you won't be running the Witcher 3 at 90 fps, but it's definitely possible if you make a game that is more stylized and less photo realistic.

They're also apparently using some kind of frame interpolation to run 60hz games at 120hz. How well that works to stop nausea I don't know, but the reviews from early demos I've seen look promising.