If they can reproject 60FPS to 120FPS in software what make you think they can't re render 1080P to 4K in hardware?
The fact that most people don't even have a TV with an 4K capable HDMI port that can also do 60fps.
the adoption install base is
720p > 1080i >>> >>>>>1080p >>>>>>>>>>>>>>>>>>>> 4k 30fps >>>>>>>>>>>>>>>>>>>>>>>>>>>>> 4k 60fps