Ok, I wanna ask this question. I have seen on the game map that forests do not use a fixed tile layout, but the trees are placed randomly which looks great. Modders will want to do that too!
In Civ4, forests and jungles were randomized in this way but the modders could never figure out how to do that, and so you often ended up with some very goofy looking alternative flora tiles with a very strong, artificial tiling effect. Please give us access to random model placement on a tile in some form, even if it's not in the editor.