When you get old-enough, a cochlear implant is exactly that.

I haven't tried them yet, but to my understanding this is a key selling feature of AirPods.

Any chance anyone knows how successful these are at noise cancellation (without the use of music to drown out said noise)?

All noise cancellation is much better at canceling low frequency noise (like the engine on a plane) than voices, for example, which it mostly just muffles. For example, I have music playing in my house right now. If I put in my AirPod Pros and turn them on, the music gets quieter but I can still clearly hear it.

I find that on my over ear headphones, the physical barrier of the headphones blocks out a lot of higher sounds to some amount and the anc kills the low sounds. I can still hear stuff while I'm not playing sound but when I turn on music I can't hear anything around me.

Yes. Closed back over ears are definitely the most effective way to block external noise. And I've heard of people wearing over the ear protection over noise canceling that works even better. For me, basically the only time I really care (or want to be that isolated) is on planes though and I travel really light so over the ear headphones is a non-starter.

I love my AirPod pros and they do a great job getting rid of background noise. But I’d love a complete absence of sound (temporarily!)

I've done a few 30 minute sessions in an anechoic chamber, which is completely devoid of sound, and it's not as pleasant as it sounds.

You hear a lot more that's going on in your head/body, and regret not wearing earplugs to those gigs you went to years ago.

>personal safety be damned

Apple is working on fixing that. There is a setting on ios 14 that can alert you when it hears things like a fire alarm, dogs barking, people yelling, etc.