At bare minimum, if you're talking about a 3D VTT, you would need basic maps for all terrain types. For enhancement, the maps would need placeable objects (trees, houses, stones, etc) that could be moved around to change the maps up to give variety o the battles. You would need 3d meshes of every monster in the bestiary books, though reskinning and resizing would help cut that down a little. You would need male and female versions of all races in all class combinations, plus alt versions to represent friendly/ unfriendly npcs.
I can see this possible being done by a small crew, but it wouldn't be easy. If you added in combat mechanics, animation, all the possible spells and visual effects, leveling, equipment choices, sound, scripting, adding in content for more than one rpg type(fantasy, scifi, modern,etc), I would say it would be almost impossible or would take a very long time
As a last note, you can do all the above already with Neverwinter 1. While the game is set to 3.0, you can use it just as a VTT in edit mode and use normal normal non CRPG play for combat, plot, etc, and recreate just about anything that a VTT system can do, but in 3D.
