Don't want to make you scream, but what's the chance of a tiny amount of animation on trees and grass, enough to make them 'sway in the wind'. Is that possible with this kind of system?
Completely possible, and also my intent (we seem to be aiming towords the same thing here).
The trunks at close range are merely models, and could be loaded via animmesh. All I (we) would have to do is change the leave positions stored in the tree structure to be the positions of the bones (or relative positions to that bone whever it may be in animation). The leaves can have a pendelum type of motion by rotating the leaf texture. For more variety, I can use multiple surfaces (randomizing between the surfaces for leaf assignment) and simply rotating the different textures at varrying speeds/degrees.
It's all possible, it's just going to be a bit of time. bare with me :-)