You can simply write an ffp shader with smee2 that can deal with much more than 3 textures. But I find 3 textures plus shadows sufficient for a good terrain. I can use sand for the beach, grass for the nature and rock for the steep slopes. You can also mix stone and sand, or whatever to create mixtures of those 3. Why should I use more?

Nevertheless a good terrain editor is really useful. Torque's editor or freeworld 3d show how it can be done. IxeX2 is for 3dgs and could be used as an alternative. GameEdit will support this as well. But I have no idea when it's done.

If you need a good terrain, just make it with one of those tools or wait for GameEdit.