A flash in the pants idea was a 3D terrain generator ... in commodore 64 bitmap mode.  There would be concessions like a greatly reduced number of polygons.  It's almost more practical to do it in character graphics.  The key evolutions would be Z buffering, clipping, supporting 320 pixels wide.  Some C64 games already implemented bitmapped terrain generators.  Pretty sure they all used a subscreen area definitely under 256 pixels wide.