You're simply asking to import 3d models from apps like blender, and I feel that would boost the quality of custom maps.
Yes, I reckon this game would be much better if we could make bigger, more realistic maps, with better buildings that we could go inside and explore.
I reckon that blocky maps such as most maps on there make buildings impractible, as walls are too thick there is no detail so it is harder to find your way around.