I agree that it CAN be done. It COULD be really cool. But in reality, it is just a PITA for everyone.

If all you had to mount to the TV was a Roku or Apple TV, maybe go for it. But remotely locating the equipment on your list is ideal. Motorized is a no-brainer, however has its caveats as well. The biggest one for me, is that none that I can see, after a quick search through my normal sources for such things, tilts vertically at all. Being above a fireplace, normally, you would tilt the TV downward. Depending on how high the mantle is and how far the seating is, this may or may not be a deal breaker, but something to consider. Now I am not 100% sure why most TVs mounted above seated height seem to be tilted downward. It seems to be the norm. Maybe to reduce glare from lights or windows? Maybe because the viewing angle is so bad that the TV image is all wonky at that angle?

Also, if you draw up something showing what it looks like when the TV is away from the fancy stone wall, and that there will be 2-3 large black boxes showing, your decorator friend might have second thoughts about what she is really asking for.

But as always, and mentioned above, its all about what the customer wants and is willing to compromise, and pay for. Deal with them directly, and inform them well enough to make the decision. Do not let the contractor or ID make it for them.