Ubisoft's Watch Dogs has been signaling the next generation since before it was even officially announced. Now that the company got confirming it for PlayStation 4 out of the way, it can start to open up about the features that will take advantage of the increased horsepower.
In a developer diary on the PlayStation.Blog, senior producer Dominic Guay explains what the team is aiming for on the new platform. He said that the city size will remain the same across platforms, thanks to the scalability of the new Disrupt engine. But on the PS4, Ubisoft is aiming for much more density in the city, with details and moving parts to replicate the activity you'd find in an actual city.
It's also taking advantage of the PS4's focus on connectivity, as Guay says they want players to be "surprised" by multiplayer without fiddling with menus. That sounds a lot like players popping up in your game unexpectedly, a la Journey. The video also mentions the PS4's social sharing features, though by all accounts that's built into the system and not optional on the part of developers anyway.
Presumably, many of these features will be included in the PC version as well, since it's the lead platform. We would also expect many of the features to apply to the next Xbox version as well, but Ubisoft hasn't formally announced that yet. Maybe after May 21 we'll know more.