Proper gas planning does not stop a diver running out of air. It only lowers the possiblity, you cannot reduce that possibility to zero. So the contingency then must be to swap.No, it's not reasonable to assume that. Many who dive with 2 short hoses either do most of their dives solo or only with other sidemount divers. With 2 independent cylinders there is almost zero chance that a diver will need to get air from another diver if proper gas management is being done.
Ask all of the short hose divers how many ever practice cylinder swaps and you will get a very low positive response, if anyone does it at all. And a cylinder swap can only be efficient if it is practiced with the same partner. Trying to swap with an unpracticed partner will not go smoothly.
However it is part of the IANTD standard to practice cylinder removal and you are an IANTD instructor. If this is basic drill in the course then divers should be comfortable performing this skill, wouldn't you agree?
I consider myself well drilled on cylinder removal; admittedly for stages as at the moment I dive BM. But I would also expect all divers at the same level to be as well drilled. I don't think that is unreasonable.
I thought the point of SM was to get into places BM can't, and that you practiced changing cylinder positions to achieve this?