FG,
You are the first person I think to ask this question.
I've been pondering this since it was first brought up on this thread as I don't know how all those screaming for it propose to do it.
To give you an idea of civvy regs a cargo compartment fire extinguishing system must fill 5% by volume of the compartment with extinguisher. A suppression system must the maintain 3% by volume of extinguisher. This will typically mean a high rate fire bottle followed by a low rate bottle in a sealed compartment. Those compartments certified for carriage of live animals will have a ventilation system that will shut off and isolate the compartment in case of fire. The detectors are smoke detectors not heat detectors. I know a bit about the Nimrod and don't know how you could achieve a credible bomb bay fire extinguishing system.