Hi @Magictwanger
I’m not a Sonos engineer/designer. However, prolonged extreme conditions (emphasis on extreme) will impact any speaker surround causing it to degrade faster than those speakers in a more moderate environment/climate
An interesting fact is that speaker surrounds can degrade in a moderate environment for lack of use. Movement of surrounds acts as a lubricant (if you will) to keep them flexible. That said environment is not the only consideration to ensure the maximum life of a speaker (components).
In the end virtually all flexible plastic, rubber and polymers will stiffen and harden with age. Kind’a like humans. LOL.
If you want a definitive answer I suggest you contact Sonos. However, you probably get answer similar to what I’ve written. JMO.
Cheers!