Nice one hallatore.LOVE IT 
I like it. Great idea.
It’s now 1 week since I got Unreal and about 4 days since my first c++ project 
(I know C# from before)
Experience so far.
- UHierarchicalInstancedStaticMeshComponent is the way to go if you want a lot of instances of a single mesh.
- HierarchicalInstancedStaticMeshComponent->UpdateInstanceTransform(…) needs some optimizations, and it need to have some sort of batch update method.
- I need to get better at rendering stuff in the distance. The kite demo has MUCH better trees further away than what I have
Here is a screenshot of the procedural forest. It never ends!
Just a quick update on the performance of HierarchicalInstancedStaticMeshComponent->UpdateInstanceTransform(…)
I forked the UnrealEngine source and look and behold! I now get no freezing when I update a lot of instances.
I wonder if my pull request will be accepted.
Current vs. modified source code. (Frametimes is how long it takes a frame to render. 17ms is about the same as 60 fps)
This scene renders at about 30 fps. Mostly because of the grass actually.