Great idea, and the preview icons also do not update quickly,
but I wish it also had a material randomization option, instead of adding the same tree model again and again just to vary their materials (colors and textures) we could have an option to include secondary materials and decide the percentage of randomization.
Landscape materials should also be able to hold 20+ layers too as default, right now after 8, you need a lot of material skills to make it up to 16, after that they start to fail when you package the project, and sometimes landscapes, specially on islands, they require lots of layers.