WOW, cool fortresses guys!
I'm still working on the next version. Currently, I have a way to specify a different shapes for buildings depending on nearby walls or other buildings. For example, chairs will now face a table if next to one. It not next to a table, but next to a wall (a throne room for example), they will face away from the wall, and have a bigger back and arm rests. They will also have a slightly different shape if in a corner, facing away from both walls on a diagonal. Doors and floodgates fit better to surrounding walls (and floodgates get switches on them to open them), chests and cabinets are places against walls, and wall grates and bars are also improved.
I want to setup the same system for walls themselves, but will have to modify the code a bit as buildings and walls are handled differently in DF. It will give walls directions just like ramps have directions. With this functionality, you would be able to have wall shape altered depending on the surrounding walls, allowing for diagonal passages to be navigatable in Minecraft. However, doing the lookup for this will probably cause the conversion to take more time, as walls are usually the most common tile type. I'll probably add a setting in the settings file to turn it on or off. Additionally, there are 256 possible wall configurations surrounding a single wall tile, and I most likely not going to implement all of them, especially when you consider you would need 256 for each possible material type (stone, obsidian, wood, 'vein', etc.)
Hopefully I'll have this finished up in a few days.
Talking about material types, right now I'm doing basic material conversions, but the settings file has support for more advanced conversions (the same way trees and plants are currently done). In theory, you could specify a different set of 3x3x3 configurations of walls for every different Dwarf Fortress stone type.
There are two different ways I could see going with this. 1. 'Realistic' - only use 'coal ore' in place of lignite and bituminous coal, replace gems with diamond, replace magnetite (and other iron ores) with iron ore (what to do with other metal ores?), etc. or 2. Replace materials bases upon color, so, granite would just be plain stone, diorite may be stone with one coal ore on the surface to color it darker, while marble and limestone may have a white cloth block on the surface, and jet would have one obsidian block, while cinnabar and bauxite would get some redstone ore.
Realistic would be more if you wanted to 'play' the level in Minecraft, but the 'Colors' version would make for better looking converted maps, as fortresses that used different colored stones their construction would now show up.
It is going to take a lot of work to setup these material conversions, as there are about 300 different materials in Dwarf Fortress (and that isn't even counting tree and plant types, just rock, sand and dirt). If anyone was to help write conversions for different material types, I'd greatly appreciate it!