I'm currently working on improving the vegetation a bit in my game engine CopperCube. It looks better already and it can be moved by the wind, through a shader:
I was thinking about making this working exclusive for the grass in the terrain, but decided that a more generic approach would be better: Just click a checkbox on any material, and that thing will be moved by the wind. That way, also the leaves of trees can be moved too. Maybe also flags or similar. I still have to make this work well with the rest of the material system, so that it also works with lighting, fog, and other platforms like WebGL and Android, etc, but it is a nice start.