This is exactly the reason why I have decided to not upgrade my HDD in my PS4. I currently have the 500 GB model C version and I am usually having 400 GB of that used. My mindset is "If I have that many games in my backlog, then it's time to stop buying games and play the ones I have."
About one minute after getting platinum on Mad Max, I erased that sucker. After making a save backup of course.
And almost all of my game purchases are physical, because you don't really own it unless you can hold it in your hands, lend it to friends or sell it.
And has Sony said anything about transferring your games from OG PS4 to PS4 Neo? Is it even possible?

Hey! They got SONY on my amiibo! Wait a minute. Two great gaming tastes that game great together!
Switch FC: SW-0398-8858-1969