Though I think it could be a great idea, I wouldn't think there would be a demand for it. Maybe a niche market, but no demand (I'm talking from my pov only).
Before further consideration, does anybody know or is there some statistics, of how many players have acquired a home other than the starter inn rooms? For what I gathered among my friends, not many people are interested in housing since they think houses add too little to the game in terms of functionality. Making a house practical is quite expensive and they prefer to spend the time and money in something else. So based on that I would say demand for house decorators would be (or is) very low.
This would be a really interesting thing to implement, though probably fairly difficult if you wanted the furnisher to actually suggest items for your house. I would definitely love to decorate other people's houses, though - I've spent ungodly amounts of time on my own already.
A potential but probably excessively expensive (in terms of real money) way to do this would be to give the furnisher a budget in crowns alongside your style preferences and specifications, have them decide what furniture would fit in your house from the crown store that fits that budget, and then buy the items and pile them in a corner to let the furnisher arrange everything.
It's also somewhat limiting when it comes to items only available with gold or from achievements, but there's no reason not to also send your decorater other items you might want included, or give them a gold budget as well.
For some people like me who lack imagination I would hire a decorator. Only issue is im a broke mother f so yeah...