A thought occurred to me: a tileset construction kit (TCK).
Basically this would be a set of minimalist tiles with some sort of textured roof and floor, plus plain, flat, grey walls. What you have instead of textured walls are sets of wall placeables that you can attach to carefully placed hook points along the grey walls.
For each set of placeable walls, you'd need:
- corner column
- normal wall
- wall with a door opening in the center
- wall with stairs up
- wall with stairs down
So, a minimum of five placeables per set.
It would just be necessary to make sure that each set used walls that are consistently the same height and that one end of each wall is slightly higher than the other (so you don't get that shimmering effect when two textures line up). If they were built and styled correctly, you can then slot the pieces together like lego bricks. The main drawback is that the wall textures couldn't be changed from the toolset--you'd need one set per texture.