Blowing Hot & Cold
It's a while since I filled a SCUBA bottle but I'm not sure that the air will heat up if you are charging the car from a precharged, ambient temperature bottle bank (rather than directly from a compressor) ? A further slight cooling all round (Joules Thomson) seems more likely.
In any event - airbank or direct compressor - some reasonably smart engineering should be able to press a heat pump into service, at least in colder weather (you could heat the house?).
Not sure what you do in hot places, say like the Middle East. But then again, maybe they don't really care about stuf that doesn't need oil..