The vegetation system comes along quite nicely, there can be defined several layers of vegetation objects, for example trees, grass and rocks, no limit whatsoever. Each vegetation layer has 3 levels of detail for its objects, 3D model, 3D impostor and 2D billboard/impostor, the radius around camera and other many parameters are tweakable, so you can make engine profiles for low/medium/high machines, depending on power. The vegetation objects can swing in the wind, in the future the trees or other vegetation objects will be breakable, the problem is a little bit more complex, because it must switch off the instanced object and create a new dynamic/broken one in the scene, but its doable.
Here is a small tease of the terrain and vegetation (the assets are ugly though, no time for that now, only tech)
Vegetation objects
Vegetation 2
Vegetation 3