Something that would be a great time saver for baths especially: a CSS system for surface textures.
Imagine that when you place a surface texture (or any item with an editable texture) you assign a variable for the texture. For instance, all the wall field tile is X, the bullnose is Y, the deco band is Z, the room floor is A, the shower floor is B, etc.
Then, you assign a texture to each variable, in a cascading style sheet.
Later, when the client says “what would it look like if we used black for the trim, instead of grey?”, you can change _all_ the trim at once, instead of changing each piece individually.
I thought of this after waiting 10 minutes for a rendering to complete, only to notice that I’d forgotten to change the texture on one area, so I had to go back, and do it all over again.
