They brought the deadline forward because that have changed the "vaccinated" criteria. It is a good thing I agree that they aren't extending it even with this and I am very happy that so much vaccination is happening and that lots of people are being given some protection. Personally I would prefer to see the vulnerable fully vaccinated and not have the enhanced mutation risks of a partially vaccinated population.
Same areas may be offering for the first doses way before that, some won't. Most places are doing incredibly well but I know of an extremely clinical vulnerable person in Scotland over 80 who still hasn't been given his first vaccine. He was desperate for it and now he's fallen and gone into hospital. But anyway, no cooperation between countries will accept half a vaccine as someone being vaccinated. Even if it were 80% effective, which it isn't. (76% with AZ and v. small and biased sample size, No proof that it lasts with Pfizer after a peak of 52% from first dose. This one is the concerning one as it is still a large part of the stock but is being treated the same as AZ though it is not. We may end up with zero protection by the time they get to dose 2 so that one isn't effective and we are more dependant than we need to be on the autumn boosters. But by then the gov might be justifying mix and match anyway).
Back on topic. I think an august trip is unlikely. And I think you are 100% correct with your last line about nasty variants.