Most simple pressure regulators will not fare well in the environment, either, because of the bidirectional flow, etc.
The "Y" hack definitely has use, but finding matches and keeping patients matched definitely means we will only be able to use it sparingly.
If COVID evolves into multiple strains, then there is a real risk of cross-infection that would make the immune system forced to work harder? Moreover, a lot of the pneumonia deaths are not due to covid itself but rather due to opportunistic infections (often bacterial) that end up causing the pneumonia that causes death. Letting two COVID patients share a ventilator could mean that now one is exposed to a novel bacteria in the other that causes them to develop pneumonia.
I'm sure they can figure out how to re-use ventilators, but there probably needs to be some kind of assurance so that things can't cross.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
The Ventilator just keeps them alive for a few days, but there are other bodily systems failing and causing death.
Lastly, I would imagine that some common pressure regulation values could be used to compensate for different sized people.