Tricky part is there aren't any practical scalable chemicals that have a handy phase change near -130'C, (in the same way that liquid nitrogen does at -196'C) so any system to keep patients there would have to be engineered as a custom electrically controlled device, rather than a simple vat of liquid.

Phase changes are also pressure dependent; it would be odd if 1 atm just happened to be optimal for cryonics. Presumably substances have different temperature/pressure curves and there might be a thermal/pressure path that avoids ice crystal formation but ends up below the glass transition temperature.