Ok, but no one have seen some big world in A7/A8 with all the stuff you said.
But i agree, i think the last Unity 3D demo could be done
i think with A8 and use of clever LOD, some portals, and
the use of shade-C for shaders.

I know it's lot of time of work with A8.
The strenhght of Unity is that it have aniamted model, grass ,trees, etc ... you can make and test some big terrain level in some 10 minutes wihtout coding : Well workflow is not the subject of this thread

A8 can do it.
The only probel A8 is for coders mainly and people using it are coders mainly.
So don't expect to see as beautifull 3D games like in Unity.

But it can do it if you have skilled 3D artists with you !