1) Would help modders create 3D objects fitting the vanilla world.
2) Would encourage modders to create their own 3D objects for entities.
3) Would encourage modders to share their creations, leading to joint modding efforts, all with the benefit of being streamlined texture wise.
How:
Release the material library with a specific license that objects created with any of those materials can be used only in Factorio in the form of a mod (yes-no-maybe);
Reference for why I got the idea to suggest this:
http://www.factorio.com/blog/post/fff-78
