Is it really hard to wear a mask…… ? Answer after considering wearing it when it is 39C.
Working conditions are primarily why no one at work wears one. There is the odd exception both individuals and places, but working inside an aircraft that's 30°+ with no airflow isn't one of them. Especially factored in with the ability to quickly and effectively communicate with each other.
The portable breathing devices you suggest is far fetched nonsense though, and if they have their own oxygen supply then that is helping to restrict the availability where it is genuinely needed. (21% of the atmosphere is oxygen, so you only require extra if you are unable to breathe properly).
As for having to demonstrate vaccination, that I have no problem with
although I do appreciate that not everyone is able to be vaccinated, pregnant women for one, so for those people there has to be an accepted level of risk in what those people choose to do, so it would not be right if the so-called vaccination passports were used to victimise those who cannot or will not be vaccinated. That's the responsibility that comes with choice.
It may well be that in the not too distant future, children are routinely vaccinated against TCV along with MMR, Polio and BCG jabs. We were given the flu jab every year at secondary school, and unsurprisingly, every year half the school got flu as a result (this is why I haven't had the flu jab since I left school, and also why I believe that it isn't news that people can still catch TCV inspite of being vaccinated).