Good topic. I have been requested the same thing, but on top of that, he also wants the neck to be made of mahogany, and an ebony fretboard.
I explained him that with the truss rods we have available it might not be a good idea to have an 18mm thick neck. I told him it only leaves 1.5mm of wood behind the truss rod. That it might work if we make it a little bit thicker, 19mm, only 1 mm more. Haven't heard from the guy since.
I guess it's better this way, i don't have the patience to deal with people who are so **** who just can't or don't want to understand this.