Nothing.
I view 16GB of RAM as disappointingly low amount that would not enable creating of dramatic new nextgen experiences.
Why? What do you think they need more ram for? I can understand more bandwidth but for the price of RAM these days I just don't see the need. More computational power is much more important in my opinion as long as they have the bandwidth to feed it.
Ram always was the big limiting factor at the end of the previous consoles life cycle but is it still? Are devs struggling with the RAM in current consoles ?