One thing that I did for myself, that I thought would be cool "official" addition. I've separated the shadows dropped by the walls into separate 4 tiles, that have a bit of alpha transparency for shadow part, and are otherwise transparent. Now I can draw all my rooms with using only 1 tile for the floors when prototyping and it makes it easy to update them, and when I'm done I just add the shadows on the separate layer as needed.
With this approach I can even have walls drop shadow on some items where it makes sense, for example I can have shadow over this carpet.
You could add it to room builder above all the floors. I've seen that done in some other tileset and it's really cool! And if I now want to replace all the floors in a room I can just use fill tool, and I keep all the shadows.