Hard drives are cheap....you can pick up a 160Gb internal for a PC for around $60, so I'm pretty sure a bulk buy of millions of them could be picked up for $'s by MS or Sony.
I have the feeling that GTAIV will require a HDD, just going on the comments for Rockstar about the lack of HDD in the Core 360 is creating problems and would limit the full functionality of the game. So at the very least I would expect a somehow cut down version of GTAIV without the bells and whistles for Core owners with the full version requiring the Premium or Elite.
Now this would certainly annoy me. You have a console and it should play the exact same regardless of what model you have. The Core IMHO is a waste and it WILL be phased out sooner rather than later...although I reckon MS will keep it going in the meantime to allow for as many sales as possible especially after a price cut.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)
