On the basis they are suggesting even those who are vaccinated can still carry the virus and infect others, the potential here is that no one will be able to travel for a few years without a test in the UK prior to departure and a test overseas prior to return.
That in itself present hurdles that the majority of people will not bother with (eg minimum £100 per pax at each end for testing, time away from work/school for testing, risk of finding out one of you is positive the day before travel, what then happens to the flights/holiday? risk of finding out you're positive the day before returning, meaning local quarantine for 14 days, costs associated with that).
The trouble is, it demonstrates the Vaccine will significantly reduce those taken seriously ill (between 70 and 90%) but it will not necessarily provide a route back to what we considered to be a normal life. The vaccine of course only protects the person who has had it, thus the important thing to any country will be whether that person is carrying it. In a way Spain largely don't care if you as the visitor are at risk, they care if you are bringing the current or any future mutations into their country. So the vaccination passport sort of become pointless.