We are receiving similar requests surprisingly often, but there are a few technical problems with the export, in addition to relatively poor gain/effort ratio in current state of things.
How would the size to export be defined? Right now the mesh resolution stops at few centimeters, but you'd probably need a whole area in full detail, surrounded by a progressively reduced resolution terrain. I also expect it to be difficult once proper procedural or semi-procedural trees arrive; basically the export would have to expand everything procedural into separate objects.
A large portion of how the terrain looks is also due to the atmospheric and ambient lighting used, so results of the export may vary a lot from what is seen in OT. Also we'd need to match the material definitions, although it may becoming less of a problem with physical lighting being used more nowadays.
I'd actually love to make a world creator based on the engine, with ability to create and fully modify the world and use it for production, but unfortunately right now there's not much space for it.
