See point 3, once most of the population has been vaccinated the risk factor should be acceptable as a vaccinated traveller with a negative test result is very unlikely to have the disease. If he does, and the vaccination rate in the country he visits is high, then he is unlikely to pass it on.
After being vaccinated, anyone who catches COVID is unlikely to get very sick. A few cases here and there is something we’re going to have to live with for the foreseeable future but mass waves and hospitalisations with hundreds of deaths per day should be coming to an end.
Some countries such as Thailand are highly dependent on foreign visitors and need to open up soon, Australia less so but it can’t stay isolated forever.