There will be a full announcement later today, but basically, anyone from within the Common Travel Area who has had two jabs of an approved vaccine, and two weeks have elapsed since the second one, can enter the Island, from 28th June, with minimal formality. IOM residents can go in the opposite direction on the same basis. People who don't meet these criteria must follow the current rules i.e. family members, new residents only, with isolation until a negative test. There will inevitably be some 'small print' but that's the gist of it.
These changes should see some uptick in air travel, but it's clearly hard to quantify. Depending on what happens in the UK, in the coming weeks, this should only be a fairly short term, interim step.