I think probably one of the most allowable instances for a writer to be permitted to stipulate slow motion would be in a comedy script where the usage of slow motion is meant as a comical cliche. I can't count how many times I have seen a spoof in various comedy films of the following now-hackneyed film moments:
1) The oft overdone Arnold/Sylvester/Bruce moment of slow motion running toward to camera (often in a state of physical disarray--ripped clothes, bruised/bleeding face, maybe a hint of a limp) from an impending mega-explosion that will take place behind him, and which will then cause him to summersault forward in the air toward the camera. (I think even Homer on "The Simpson's" did that once!)
2) The scene from "The Right Stuff" where about a dozen astronauts are walking:
-- side-by-side
-- in slow motion
-- in their space suits
-- toward the camera
3) In THIS example, there are several variations on the context of what it is that the Protagonist is actually trying to prevent, but the shout of "Noooo!" and the forward scrambling with arms outstretched is always the same ......... Some valuable object is falling from a precarious height, and the hero sees it's about to fall, and he leaps forward in slow motion with both hands extended, trying to catch it while, shouting "Noooooooooooooooooooo!"
4) A man and a woman start out at opposite ends of a sunlit meadow that flits with butterflies and is adorned with wild flowers. And then, arms outstretched, they begin to run toward each other in slow motion.
5) Running slow motion on the beach (or sometimes slow motion running anywhere, really, no matter what the comedy film is) with THAT monumentally famous music playing from the film "Chariots of Fire."
Surely ALL of the above were written right into those many comedy scripts with the blatant stipulation of "slow motion" unmistakable inserted by the writer directly into the action paragraphs.