Many also do not. Maybe even most?

I typically fly one airline so it could just be their planes, but I don't remember the last plane I was on that didn't have outlets[1]. And certainly the folks that can drop $3,500 on this are more likely to either be in business class or flying "nicer" airlines, so plug access feels like a non-issue to me.

[1] That being said, the number of times a plug has been able to support a charging brick directly is...miniscule. They're usually so worn out that they can't support the weight, so I have to carry the extension just for that reason.

Usually very limited amperage, almost certainly insufficient to keep this thing going indefinitely.

This is not true. Most seats have a 120/240v receptacle that can keep laptops charged while in use.

You’re forgetting this thing uses a mostly passive M2 chip. Not to mention I’m sure they designed it so it could be powered from the USB c ports on their laptops. The headset won’t use anywhere near the amount of power you seem to be implying.

That's voltage, not amperage. Just because it's a 120V receptacle doesn't mean you can draw large current. My laptop charger gets booted off the grid pretty frequently on a full plane.

Even if it's limited to 1A, 1A/120V must be enough. It can't have loud fan so must be power efficient.

I wouldn’t assume you can draw 1A.