Separate decor definitions for different plane types
The ability to define separate decoration definitions for the same graphic depending upon what plane it is used on. A def to be used when the graphic is used on the floor, another one for when the graphic is used on the ceiling and another for walls.
Perhaps a flag like dcf_pwad etc?
Naturally, to maintain backward compatibility, the default would be to use the same decoration def for all surfaces (i.e. if none of the new flags alluded to above were present).