Jet II you don't happen to have any sources of information for that do you that I could perhaps read over at my own leisure?

Try this briefing from FedEx

Not specific to water mist systems but it explains many of the same issues. Even gaseous systems have problems adequately penetrating ULD's so any liquid system is going to have a much harder time. The FedEx idea of puncturing the ULD could work with a liquid system but then you have the issue of false alarms. If a false alarm is triggered and the system activated by spraying water over the entire cargo you could easily have to scrap everything. If you activate a gaseous system during a false alarm then the cargo is undamaged.