Many COVID measures are by and large about liability avoidance on part of those in charge. Just because, you know, if someone gets sick, their lawyer might decide that the local government, the airline, the company management or whoever else didn't perform their duty of care and that's why poor chap got infected. That's why I think that the very earliest we can talk about ditching the masks on board is whenever the WHO declares that the pandemic is over. That's the best-case scenario. In a less optimistic scenario, nothing will change in our lifetimes, not to the least because there are communicable diseases other than COVID which can hypothetically be passed on an aircraft.