It seems like that would take away any rehabilitative effect prison might have. Convicted of a crime, go to sleep, wake up ready to continue committing crimes.
Except that prison doesn't rehabilitate at all: it does the opposite and makes people worse. The rehabilitative theory of justice is essentially nonexistent in the US, nobody even pretends. Instead it's about punishment/retribution and "keeping them off the streets" during the period of their sentence. The coma solves the second concern, but isn't cruel enough to solve the first so I don't think you'll ever see it accepted in the US.
