FedEx Pallet blanket.
SNS3Guppy--- although you are informative, educated and experienced in both flying and fighting fires, I believe "ClassC" has a few valid points.
The industry needs to change, upgrade, spend money, ect. Whatever it is, they need to sink money into it. Those with the money to upgrade will survive, those who don't, wont. You suggest a hull loss may be cheaper to the operators than upgrading, but what if the UPS 747 were to have taken out an apartment on the way down?. I'm sure the insurance industry will always be monitoring their exposure to liability, and not just the hull ( and crew ). Costs will rise on those whose "exposure" places them at higher risk.
I also fly international, cargo with limited suppression on the main deck ( none ). Unlike you, I can't say that fighting a fire on the main deck would be useless. You do paint a pretty ugly picture of what a fire will progress to, left unchecked. Why not try to fight it?. It may be "readily accessible", or it may not. You "may" have the excess crew available to accomplish the task, you may not. If your mid-way over the pond, even if "extra" crew is unavailable, you be you ass I'm gonna try. If it reaches the point of "too hot to even get near", or "can't locate source", then I'm screwed. I'll deal with that as well.
I guess what I'm trying to say is, use you knowledge to help us plan to deal with it, not just paint a scenario of doom.
The FedEx fire suppression system is a great start. True, it won't apply to my airline, as we have pallets on the main deck. But the suppressive "blanket" over the pallet is a great idea. The only downside I see is that the "blanket" may delay discovering the fire.