As an illustration of how far this could go; why not turn off one engine at the top of descent? I mean, you're going down anyway aren't you? Then at say 10,000 feet, fire it up again for the landing.
Apart from being a dumb idea, I think, the cost of an additional start cycle on the engine will probably out weigh any savings in fuel.
Can anyone find, in the AFM or SOP of any aircraft or company, where coasting into stand all engines off as an acceptable procedure is discussed? Thought not.
Personal opinion but the potential for things to go seriously wrong whilst still moving but all engines off is way too big to even consider it.