It's going to be the same jump as last generation or bigger. We've had more time between generations and going from 720p to 1080p is a smaller jump then from 480p to 720p. And most games will probably still be 720p next gen. That leaves a lot of room for graphical improvements especially for open world games which have been severely hampered by memory limitations this gen. Draw distance, lighting, shadows, reflections, pop up, smoke and particle effects will all see dramatic improvements again.
I already think Skyrim on PC looks vastly superior then the console versions. Sure up close the difference is not that bad, but look out into the distance and the difference is huge. So without any extra polygon or texture work it will already be way better.







