The blue light (status LED) goes out on my Ace when I’m wearing the headphones. Admittedly it does show when I remove them from my head - I think that’s okay as it reminds me to power them off. Maybe power them off before you remove them and then the light will then hopefully not show.

Not to throw shade on your request… so I assume you’ve already experienced the supposed annoyances you mention. As for a plane I would definitely (and have) found the overhead reading light disturbing when used by another passenger so I find it difficult to see how the blue LED on the Ace would cause a similar annoyance. The intensity of the blue LED is no where near in comparison.

I’m doubtful Sonos is going to put in that feature as it’s rather important to letting the user know that the device is on and using battery.  As @Ken_Griffiths stated, it does appear to automatically turn off when it’s worn.

You could look in into maybe covering it with a small piece of black tape, but I suspect it won’t look good and will fall off rather easily.