The take up is high in the very high risk groups like over 80, and a bit lower as you go down the age groups.
By the time you get to younger working age people, I think it will be a lot lower, or they need additional information to persuade them to take the vaccine. Many will want or planning more children and whilst there is a recommendation to take the vaccine, some will worry that that pathway is untested (at present). Similarly, I don't see 95% turn out of parents vaccinating children either.
Many of the younger age groups have already had covid (confirmed and suspected) and many have not been that ill with it (yes, some have, but statistically we can see they are not the groups in hospital). Their perceived risk is lower, I'm sure uni students won't all have the vaccine either.
I see it as a matter of personal choice and informed consent, just like the flu jab. We don't get our knickers in a twist if people don't have the flu jab and I don't intend to worry about people not having the covid jab if most of the more vulnerable are protected, and even then it is their choice what to inject into their bodies.
As for practical levers, wanting to get a vaccine passport (however they are devised) will be a big motivator, as will any access without a vaccine proof, but for younger groups, this will include testing negative prior to, say, going to concerts etc. There won't be 'vaccinated' concerts and 'non-vaccinated' concerts.
As Covid fears drop in the population, as with flu, the urgency of having the vaccine will drop anyway. A combo flu/covid vaccine every year might be the way forward for over 50s.