>One further question ... are there plans for more arbitrary street plans to be used as a layout?
Yes, absolutely. This will be more complex to add properly, but definitely in the plans.
>Also are there plans for cities to follow terrain heights?
Yes. It's important that the cities follow the underlying terrains.
>Terragen has an SDK available. It *may* be able to do what you are describing, though it is currently limited to only creating new custom node types, you can't create new menu options for example. If you're interested in working with the SDK let us know.
I only know the existence of the SDK, but I don't know how it works, how to use it, what language and tools to use etc... The way I see how to import cities is: user adds a city importer node, loads a file from the node, node reads it and creates objects instances / populations and places the instances itself, not via Terragen's population nodes. The "problem" is those new populations would need meshes, materials and textures. And there would potentially be lots of them. Those would be the buildings, the roads portions, the props etc... each of them can be complex entities made of several parts, objects hierarchies, and use several materials. That would be ideal. A more realistic and intermediate option could be used instead... what do you think?
>As for PBR materials workflow, yes we are working toward that as we move toward path tracing for rendering.
Excellent!