Vote on the idea here and add your suggestions in the comments. I feel unity is only lacking in its terrain and im sure unity knows that there is alot missing in that area. So I hope unity can implement my ideas and many others by unity 5 which I assume is next fall
http://feedback.unity3d.com/suggestions/expanding-unitys-terrain-system
I don’t think Unity needs to worry about that area. You have some awesome plugins that solve many problems.
I recommend you have a look at these:
If you combine those two bad boys you will have all you need.
And consider combining world machine into the workflow.
Caves can be easily solved by using a mesh and a lod script like Smart LOD
+1 - if you look in the Showcase section there’s actually a thread there now about a scene of Mt. Rainer created by combining these two bad boys.