There are likely ways this could be abused that I’m failing to consider, but wouldn’t a simple approach be to create an in-game vendor that sells decoration layouts (codes), in which decorators put their designs up for sale? There could be a preview function, of course.
This honestly depends on how intricate WoW’s decorating system ends up being. For example, I think they’ve confirmed that we can clip furniture together. In FF14, to use the example I’m familiar with, a lot of what distinguished really good builders was their ability to combine different furnishing assets into really creative and natural-looking new furnishings, many of which aren’t intuitive enough to copy by looking. It’s been a while so I’m struggling somewhat to put together an example from memory, but something like “a cupboard clipped through the floor + a nightstand + the top of a pillar = a custom front door with a window, because magic”.
If we get a similar or even greater level of freedom, I have no doubt many designs will be too difficult to copy for anyone who isn’t already willing to put in the effort to decorate their own space.