Chris,
You mention your well-known guide friend and your conversation yet cite Karl Klassen in the same post, who disagree with each other. Karl, the CAIC and NWAC all use the terminology of 'Low Probability, High Consequence' because it speaks to the complexity of the problem which also includes the difficulty in predicting how and when these avalanches can be triggered. Yes, they can be triggered by another avalanche, thus the high consequence if and when they happen. Multiple industries recognize this language as something that is very dangerous and training the general public in this language starts with their first avalanche course. All level 1 courses cover this topic when discussing PWL, Deep Slabs, Persistent, Wet and Glide avalanches.
The other danger is crying wolf, and making it sound like you can trigger a Deep Slab easily then have the credibility eroded from the forecast because no one triggers a Deep Slab. The key part of the forecast, (CAC/CAIC/NWAC etc) is to use shared messaging on these problems. Karl speaks to the complexity very well and everyone else cites Karl because of this.
In ten years this problem will still be Low Probability because of its depth unless skiers become obese. What I believe will happen is over time the communication between BC riders, Avalanche Forecasting and other agencies will improve and prevent needless risk. Overall nationally, the avalanche fatality rate is decreasing except in WA. where we are seeing wide spread growth in all BC winter activities. This too will change as we adjust to the new load of users and improve communication and awareness as has happened in Utah and Colorado.