This is instead of large 3 layer sliding glass doors, the 3 other walls are brick, it gives an even sound signature, you can then add absorbers, diffuser or bass traps to that if desired afterwards. Starting out with a even sound signature and room balance, especially in the speaker end of the room is important for good sound, especially with dipoles and omnidirectional speakers. I don't worry much about flammability, i live in an old house with wood floors and ceilings, its going to burn like a tinderbox anyway. I dont smoke, don't lite candles and have fire extinguishers strategically placed. Fire is also monitored and reported trough my alarm company.
Each case is a case, we are just making general considerations about materials. Omnidirectional speakers like MBL, are in the exception section!
But yes, having conditions to avoid sound treatments is the best. It is why some people prefer well designed drywall walls - why adding bass traps when we can have natural bass absorption in the room? I suppose you admit that a perfectly rigid room will have excessive bass energy.
BTW, the large 3 layer sliding glass doors are a great bass trap!
My previous house was similar to yours, fire detectors and alarm company included.
IMO flammability can be an issue with people having listening rooms in basements or attics with limited accessibility.
