Why would this be easier?
(medical exemptions)
It wouldn't need to be easy. International travel might not be possible for those who cannot have the vaccine safely until large numbers have had the jab and transmission is suppressed (if indeed it is suppressed, not clear yet if the vaccine will prevent spread as well as making the disease mild).
But it will be clearer cut. For masks, it's not only the diagnosis, it's the effect of the diagnosis on the individual (so some people with condition X might be fine in a mask, others might not). But a diagnosis of severe allergy, or another (probably immune system) condition will absolutely preclude vaccination.
As the vaccine won't work in somewhere between 5-30% of recipients, I expect testing regimes might be in place for quite a while longer, for everyone. And for those who cannot be vaccinated, the wait for resuming n of certain activities might be rather longer.
I wonder if there might also be an exemption for those who are on trials for vaccines? Some of whom will have received a placebo but who cannot be unblinded and then vaccinated until trial concluded. Or those on the prophylactic antibodies trial - who cannot be vaccinated for the duration either. I suspect travel might not be possible for them for a while, which is a shame because without volunteeers there would be no preventative measures and it just seems a shame that those who have acted benevolently might be late to see any benefits for themselves