The trouble with systems like 'mask exempt' status is that in order to make them hard to misuse, you'd have to make the application and evidence process more rigorous. That would generate objections from folk who wouldn't accept being made to 'jump through hoops' (perhaps a poor analogy !) to receive adisability exemption - something to which they are entitled.
@rseholes abuse the Blue Badge system, where the entitlement cards are large and made of plastic, so not that easy to fake, and even though there is a photo of the qualified person, it is on the side that faces down on the dashboard, so some rats use them when the qualifying person is in no way involved in the trip. Some folk then criticise the scheme as being too open to abuse, instead of hammering the b@stards who abuse it (not suggesting I've seen that on this forum tbf).