When discussing the detonation, I simply chose the wrong word. The word I should have used is Deflagrationwhich are thermal processes that proceed radially outward in all directions through the available fuel away from the ignition source. The description of what I was talking about is sound, I just used the wrong word.
In regards to the positional sensitivity:
Trail Boss powder was designed to fill the case and eliminate the issues of positional sensitivity. The IPDA (International Defense Pistol Association) is very acutely aware of positional sensitivity, which is why they have developed procedures for eliminating that issues with their 90 degree start. (not specifically for trail boss, but for powder in general.)
While Trail Boss is touted as being positional insensitive, there are differences in FP/S in regards to the position of the powder.
In previous Chrony testing I did about a year ago, I found that the differences in feet per second between having trail boss at the bullet end, the middle and the primer end were between 80 to 150 fp/s. That is slight enough for the manufacturer to declare the powder is not sensitive to position in the case. However for a subsonic round, especially ones that are close to the speed of sound, that could mean the difference between having a whisper quiet shot and having to deal with the crack of a sonic boom.
There is no downfall, other than time, to using the cotton as a filler and it can mean the difference between a 1050 fp/s shot and a 1200 fp/s shot - and depending on atmospheric conditions and barometric pressure, you may have just exceeded the speed of sound.
Personally, I'll keep my cotton filler and err on the side of caution.