I’m an D5RENDER user since 2.4.
Do you know CESIUM plugin in UNREAL ENGINE ?
You can import in your scene, 3D terrain from entire GOOGLE EARTH data base (building, road, terrain).
I think it will be a revolution and a “fatalaty” for your contestent to integrate it inside your next version. It will be a logical way with your Last terrain module.
And if you can add a tool who can crop the area of our project it will be just perfection
Please look at this CESIUM Soft here :