I think you need to be very careful if you think that de-pressurizing a cargo compartment is going to put a fire out. At best it may reduce the spread.
Read up the books on the early Everest climbs and you find they were cooking on meta fuel stoves above 25,000 feet, and a lot of what you carry is more combustible than metafuel.
The Class's E cargo holds were brought in many years ago with much lobbying from the aircraft manufacturers and airlines but I doubt they would contain a fire that had any oxidizers in it for more than a few minutes.
My 2c worth...