I don't really think we will have much improvements this gen - probably not as big a last gen which saw massive increases in hard drives on both the Xbox 360 and PS3 (end of gen vs launch.)
If the PS4 upgrades to a 4K blu ray player, I don't think that will affect gaming much. Sure the new drive might be a little faster, but the games are still limited by the hard drive.
And the Xbox One has the elite with it's faster drive, and you can add a fast USB 3.0 large hard drive and make games a little faster.
But all the design elements for both is the same. I don't think there will be significant hardware design changes.