We know that they are working on their own physics engine rather than licensing one like they did with Havok for Source 1. It’s called Rubikon. Maybe that means they’ll be working on physics that most standard physics engines don’t do. Maybe we’ll be getting physics based animation system kind of like Euphoria, but for all animations. Like procedural animation. I also remember Valve said they had to cut down on how the gel in Portal 2 worked because of consoles so maybe they’ll be experimenting more with liquid physics.
Also I imagine that Source 2 will support everything that UE4, Cryengine 3, RAGE, and other modern engines do, like tessellation, dof (bokeh), deferred rendering (so dynamic lighting), soft shadows, etc. I’m certain we’ll get some demos of the engine at the Vulcan presentation.