Been thinking around this movie a bit now, I don't find it that cool anymore, sorry. It can be done with the current Cry Engine, with some added code as with Doom and Unreal. What they only showed us was really a more advanced and realistic physics, that with the leaves. The day cycle is already possible in Doom, and volumetric clouds can not be that hard to implant, not soft particles either. Unreal 3x has already soft realistic shadowing.
I do belive that when this get more official status, we will see much more cool stuff, and things that actually is 100% new and not possible to this date.