I agree with Goms. That ecosystem capability is the number one thing I envy Vue users for. Built-in, random shape, animateable vegetation is just an awesome concept. I don't think vue plants look good up close, but they are great at a medium distance. Also, vue'l lighting seems to work just great with ecosystem plants.
For Terragen, it would already be a huge winner, if the user could specify a population mix of various species, at configurable densities, all in an easy to use user interface. That's my personal number one item on my wishlist.
Cheers,
Frank