In unreal I've begun to setup pcg to layout the location of ground plates, trees, bushes and grass. The PCG system does not work with splines for paths or layout buildings yet.
The rock generator takes an input geometry, currently a simple sphere, and using a set of constrained parameters generates 6 rocks that are around 2k polys including displacement, roughness and diffuse textures. The generator takes about 15 minutes to generate a set of 6 and can intake a seed to deterministically generate millions of variations using the same input geometry.
The landscape generator can take any fbx, transform it, and simulate physical processes to imitate a real world island. Input geometry can come from unreal landscape sculpting and preserves all major details, in addition it has various style parameters that are bound to reasonable value ranges.
Building generator in it's very early stages. It can take procedural box modeled buildings and improve their geometry. It will be able to simulate destruction of the buildings as well.
High LOD Output 50k poly
Low LOD Output 7k poly